Yeah, I thought it looked way too big! Unfortunately the saleslady was clueless (it's supposed to be a reptile specialty shop) and their scale only weighed in pounds, so I had to guess. I ended up just tossing the large rat, since she wanted nothing to do with it, and I'll get her a small/medium live one next. Should I wait another 5-7 days, or try again right away? Thanks for the replies!
P.S. She weighed a little over 1700g last week, so she is a pretty big girl...