Is she pregnant?

So I'm sure this is a pretty common thread, but.........

I bought two rats a couple of days ago (from the petstore). I got two adorable little girls, Hillary and Monica. Hillary is a satin fawn, and Monica is either DARK brown or black. Both are very sweet, and we seem to be off to a good start.

Problem is, I think Monica is pregnant. I started weighing her when I thought she was gaining a lot of weight, and this is what I found.

23-Apr 193g
24-Apr 200g
25-Apr 207g
26-Apr 213g
27-Apr 220g

You can see she's been gaining about 7 grams a day. I'm feeding them Kaytee brand Forti-diet lab blocks, so I don't think she's gaining weight from the food.

I'm pretty sure she's pregnant, but can anyone confirm this? If she is, I'd also like information on what I'm supposed to do. I've grown pretty attached to her, so I don't want to take her back, so I'll need advice on how to care for her babies.