I have an 18 month old Border collie bitch who has got snappy and is very dominant.
She will mark over male dogs even though she has been done.
She started to get a snappy before she had her op so i thought it would stop her from becoming dominant but it hasn't stoped her.
I wolud not expected dominance issues with a female as i thought it was a male dog thing?
By herself she is good in the car and fine out but she will copy my girlfriends dogs when she is in the car by barking.

Marking is not dominance related - it is instinctual for a dog to mark. What is she and you doing when she is snappy? Is she snapping at you or other dogs?

It sounds like you bring her together with your gf's dogs - but she doesnt live with them?

How long have you had her? How much socialisation did you do with her?

If she is in the car with other barking dogs its not surprising that she is joining - you should probably look at why the other dogs are barking.

A bit more detail may help people respond.

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Jack - Black Labrador
Nalsy & Ponch - Purebred bedwarming moggies

I live with my gf and her dogs.
Had Meg since she was a puppy.
She snaps at other dogs.
My gf works at bording kennels and Meg goes to work with her in the day so she see's other dogs all the time.
She snaps at dogs she knows and dog she doesn't know.
If she goes into a house where there is another dogs she snaps at them.
My gf's mum has a male border collie which went for her not long ago because she snapped at him and it put the wind up her and taught her a lesson so she thinks twice about doing it to him now.
She wont do it to the other dogs in the house as she knows her place in the group it seems.

Some collie bitches are just bossy and many collie boys take it quite happily. My friend has a bitch who is like this she snaps and shouts at Bobby who totally ignores her, she doesn't bite however, after a few minutes she calms down and they play. If Bobby gets too close to me or my friend she will again snap and shout.

I would love to know if there is a way i can get her out of it.
People think she's nasty when she's not...........

I'm not being unkind but if your collie bitch has become snappy its because you've allowed it to happen.
Having a bitch spayed does not have the same effect as having a male dog castrated and although I don't like the term 'dominance' female collies can be just as strong in that sense as males.
Of course she will copy the other dogs if they are barking in the car, she is only a youngster.
Are there any decent dog training classes in your area (preferably APDT) where you can be shown how to manage her behaviour and socialise her in a controlled environment?