Possible Unexpected Babies...

So I foster for a small animals rescue, and tomorrow I'm getting a possibly pregnant female chinchilla. :D

She will be my first chinchilla so I've been doing a ton of research and I feel pretty confident on care and play time.

(Her story..)
Cece (female) was adopted as a friend for another recently adopted chinchilla(PJ). The owner was told PJ was a female so naturally they went and bought another female for PJ so she could have a play mate.
Turns out PJ is a boy...
SO now I'm getting Cece as a long term foster in case the time PJ and Cece had together made some babies... (Not exactly sure how long... not very long since they got a vet visit but long enough they were together. Maybe a night? Anyone know how quick chinchillas can breed?)

Now I'm wondering if anyone has any clues they use to determine if she is actually pregnant?

I'm already planning on weighing her once a week, but she is underweight a little bit so I'm not sure how accurate it will be.

I've also heard it's not very obvious until the 3 month mark or kits show up..

And just for fun if anyone is into genetics I was wondering what the kits would look like. Dad is a mosaic and mom I BELIEVE is a standard grey but it's hard to tell from her picture. (I'll let you know tomorrow)

Thanks guys!