I really feel for you and your wife as it can be quite un nerving when a dog bites so you are obviously going to feel unsure . Lack of confidence from you (and i'm sure most of us would feel exactly the same) around an anxious / nervous dog is likely to just make things worse.

Did the rescue centre have any information about her past etc?

I would definately consult a professional.

I know its hard but don't give up on her yet.

As with any aggression do seek help from a vet in case of an underlying reason.

However don't fear her, your fear will only come across to her. As not sure about her back ground if she had been mistreated before you got her she may have been weary about things going on around her head. it is a sad fact that most abused dogs have been hit around the head or grabbed around the neck. this area in general is a vulnerable area. if she is uncomfortable it may have been a case that she hasn't made it clear previous times your wife has done her eyes that she is uncomfortable with this maybe the signs have been so subtle they have been missed by yourself or your wife. Maybe due to her young age she hasn't known how to make her discomfort known and this was a last resort. Unfortunately there are at this stage a lot of maybe's. But don't let this one incident put you off.

This can happen in Rescure or well bred dogs.

We got 1 of our dogs from rescue and she was tempremental for a short while, then when she gained trust was fine.

We got 1 dog from a loving family who lived in a pub - and because of that he got tormented so they sold him because it wasn't fair - fantastic dog - you move too quick and he'd have a chomp on you because he thought you was going to hurt us.

We got our other dog from friends who were breeders - great temperment - She got heatomas (not sure if I spelt that right) in her ears - you hurt them whilst cleaning and she'd nip you. Often gave a slight growl, sometimes not at all and NIP!!

Her daughter, amazing with people. Would like to give you a nip/bite if you hurt her when cleaning her eyes.

With my examples above from our dogs, they've come from all types of backgrounds and one bred ourselves, and all could give a nip/bite with out warning.
As I saw someone say before, your wife may of hurt her and that was her reaction because of the pain. Just teach her to trust you, please give her another chance, the next home might not be so loving...

Did your dog grown before she bit?

I doubt this was unprovoked, your wife was doing her eyes and she was objecting to that, if your dog growled first, your wife had ignored the warning to tell her she wasn't happen. As your dog can't tell your wife any other way she bit her.

How much damage was done by the bite? Did your dog break the skin?

Your dog could have done a lot of damage to your wife, cleaning a dog's eyes most people have their faces close, she could have gone for her face and done considerable damage.

I hope your wife is ok.

Without knowing the dogs past it is difficult to tell whats going on. She may have learnt not to give warnings such as growling first. Unfortunatly it is believed that if a dog growls then you should ignore it so as not to show fear, however the dog then learns that growling doesnt make you go away and they may then no longer bother with the warning and just bite. Also some people will shout at a dog for growling at them which also leads to dogs that can be slightly more unperdictable.

Dont shout at your dog for biting and if she does growl please respect her wishes and step back, in your situation I would tell her she is a good girl for growling as then she will be more inclined to produce a warning first making it much safer for you and your wife.

Id definatly say a vet check is in order and a good positve reward based behaviourist should be brought in to take a look and provide you with some advice.

You can fínd behaviourists on the links below.

The Association of Pet Behaviour Counsellors
The Association of Pet Behaviour Counsellors

COAPE
Robert's Place

hope you can get something sorted.

I agree if there is a good behaviourist/trainer near enough, were I live there are plenty of people who say the are behaviourists/trainers but are the old school and do more harm than good. I am seeing the damage they do quite a lot and several dogs have had to be pts because of the advice they received.

I went to see one trainer who was supposed to be positive, it was the old pull/yank/yell at the dogs to get them to walk to heel and a dog that though she would have some fun by racing round the hall, was hit on the head with a thick, cardboard pole, the type that is in the centre of carpets. Thankfully I hadn't taken my dog and I never went back.

Many say they are positive, reward based trainers/behaviourists but they are not. I have a friend who took her dog to one and was told to put a prong collar on her dog to get him to walk to heel. She walked out.

i do agree there are those poor old school trainers/behaviourist. i went to one of them myself claim to be positive reinforcement ie you play with the dog when it does it right but the yanking, the head thumping to get its attention is all still there.
i'm currently training to be a behaviourist for the simple reason i went to one of those trainers wanting help with aggression problems towards people my dog had. he was my first dog i knew no difference. after going for almost a year i realised that my dog wasn't improving she did nothing to help resolve the agression infact his confidence was totally knocked. i then started reading books by Jan Fennell and artictles about clicker training then i got to see all this in action i fell in love with this whole knew idea. i worked on my own with my dog several aspects of his behaviour improved the agression was a little easier to control. until he went for my 3 month old son i had to make a decision. non of our re-homing centres would take him with his agression. i seeked advise from a vet. on this occassion no amount of training would of helped. He grew up loving people and turned almost over night i knew nothing had ever been done to harm him as his character changed before the classes. it transpired that he did have a tuma in his brain that was affecting his personality apparently quite common in collies i've found out since.
Sadly i took the option to have him put to sleep mainly because i could risk any harm coming to my baby at the time.
i now have 2 dogs and i use clicker training they are brilliant and although it can take longer with some aspects of training the dog is doing it because he wants too. i also changed how i live with my dogs. They don't go everywhere with me they have thir training time they have their attention time. They live out doors during the day, they eat after the rest of the family they're not allowed upstairs and definately not allowed on the furniture. I'm pleased to say i couldn't ask for better dogs there's no agression to members of the family. Trip will bark at strangers walking past the garden but show me a dog who doesn't. if thats all i've got to live with i can't complain