Hi all! Thank you for your responses, thought I'd update you on our vet visit!
The vet was lovely, she actually shows chihuahuas herself so was a brilliant help (she specifically chose to see Vega for her appointment, apparently she gets first dibs on all chihuahua puppies that come into the vet clinic for an appointment!). She said that Vega is a dark blue and tan but normally they get lighter with age so we shall see! Inside she mostly looks black but in bright light she is definitely a grey-ish shade. She has a bald patch on her tail and a scratch in her eye which I knew about, because that's what the previous owner's other dog did to her when she attacked her

But her skin looks good (I know Blues can sometimes have skin problems, so in the clear for that at the moment!) no signs of fleas although she's still too small for the Frontline spot on and she checked her legs as well as it looks like she has a slight limp with her front left leg but as far as the vet could see/feel, there wasn't anything obviously wrong and Vega didn't seem like she was in any pain when she was moving her leg around, she was just trying to chew her fingers off

Just have to keep an eye on her scratched eye in case of infection and her limp to make sure it doesn't get any worse.
She also said she looks very well bred, perfect head and jaw which made me a proud momma indeed! She weighed her and my scales at home are obviously way off! She is actually 0.6kg so heavier than a pound, but still very tiny, little fatty

But she didn't give her any of the puppy shots, we have to go back in a couple of weeks as she didn't want to do them until she was at least 1kg. I don't mind really, I can wait a few more weeks before taking her out, I remember my little one was heavier than 1kg and she still had a bad reaction

so we shall wait. As for her age, she said it's hard to tell, she could very well be 11 weeks and just very small but in her opinion (and having looked at her teeth) she thinks she's more like coming up to 8 weeks. Which would mean the previous owner had her from 5-6 weeks of age?! Man I really wish I could see those KC papers so I could be sure, poor little mite. Just slightly disappointed that I won't know when her actual birthday is! I've always knows the exact age of all my dogs

She has a few of her back teeth and her canines and a few of the front ones but they are all baby teeth so it may just be that the others fell out and we're waiting for the adult teeth to come in but who knows, normally my chis' ears droop when they're teething and hers haven't, they're still straight up so not sure!
Thank you all for your lovely comments, she is an adorable little girl indeed. Just feel so bad for her eye and tail

At least she's in good health though and that's all I hoped for!