Some brilliant advice from ClaireandDaisy.
Lilli has had a couple of very traumatic days and really needs some space to come around in her own time.
Despite how rubbish her life was, it was all she knew and it's completely understandable for her to be confused and displaying aggression. She's been neglected, is only 2 and potentially having her 3rd litter so I can't imagine she's seen very much in her short life. Bless her.
I've found that dogs I've cared for who have been abused normally react in one of three ways in a new environment.
Some seem almost grateful for rescue, eager to explore the world around them and despite what people may have done still wear their heart on their sleeve and a big grin on their faces.
Others shut down. If they have the option of flight, they will take it but if they don't have an escape route they will just freeze in the hope that the scary thing goes away.
Some will come out fighting. If they are pushed beyond the realms of their comfort zone they will protect themselves using the only things available to them which is a growl or teeth. I think you said she was fine when she first arrived at yours? If that's the case, it sounds like she's overwhelmed, feeling completely pushed out of her comfort zone and is more than likely lashing out through fear.
From her point of view over the last few days her owner has left her with someone while they have gone on holiday, she arrived at your house, she's then gone back to the breeders house where it sounds like she's been thrown into the deep end of family life and met her parents etc. She's had a bath, a trim and ticks pulled from her and now she's on her way back to yours.
She's going to be wondering which way up she is.
I've obviously not met her but from what you've said, in spite of the bites I wouldn't have her labelled as too aggressive just yet. I suspect given some space and time, you will get to meet the 'real' Lilli and I would be very surprised if she is anything like the Lilli you are currently dealing with.
Do you have the space to keep her separate from everyone/everything until she starts to find her feet? I'm also wondering if it would be possible to arrange a home visit by the vet to keep stress to a minimum?
Well done for giving Lilli a chance. I'm keeping my fingers crossed and really hope that it works out for both you and her.
