Judging by her face and size, I was thinking she was pretty young and maybe this is her first litter. However, she does have some tartar on her teeth and her nipples seem really rough to me ... like maybe she has had a litter(s) before?

Kim, If a cat has had litters before their nipples will never be young and perky ever again! If she's never had a litter, they'd be kitten sized which barely show. Could be she's "pinking up" and getting ready to deliver. She's such a lovely dainty little dolly!