It is very likely that she's pregnant. You have to go into adopting her believing that she is.
Chinchillas gestate for around 111 days.
The best way to tell if she is pregnant is to weigh her every couple of weeks to see if her weight is increasing. She probably won't just let you pop her on some scales so I put a dust bath on my scales, set then to zero and then let Cheech hop in to have a bath. I quickly read the weight when she stopped rolling for a second.
Later in the pregnancy she will probably lie on her side a lot to get comfy. And right towards the end she will drink a lot of water to help with her milk.
I couldn't tell at all with Cheech because she lies down a lot anyway and as she was sharing a cage with her mate I couldn't tell how much she was drinking. Two babies just appeared a month before I thought they were due. Hehe, it was a nice surprise.
If you're not too sure what you're getting yourself into, I wouldn't. However if you can get advice from the breeder on what to expect, or like mine said she would come down and help with the birth if needed. Luckily mine went smoothly with no problems [in fact I was asleep when it happened and didn't even know] and I have two happy, healthy babies, but that's not always the case.
You can expect usually one or two babies but they can have more and if they do sometimes the mum can't look after them all and then you have to think about thinks like hand rearing and what milk to feed them.
Do a lot of research first. And babies are so cute but I think Cheech's are driving her mad, they keep running full pelt right into her and jumping on her while she's asleep.