Do you know if this person had/has any other chinchillas?
IF there were no other chinchillas around and she has been the only person that had them (other than you) for the last 4 months ... it is very doubtful that either would be pregnant.
Females' teats are not normally elongated unless they have had kits in the past and/or are within a month of delivery.
I would watch their weights carefully for increase.
Do not palpitate their tummies ... if they are pregnant, it could kill the kit/kits.
If you place your hand in your lap ... palm up ... set the chin on your hand and give her a treat that usually takes a little while to eat ... if she is pregnant ... you should feel a slight movement, for the first time, about two weeks prior to delivery. Do this daily.
Within 24 to 48 hours of birth the momma chin will usually increase the water intake considerably.
How can you tell if she is in labor?
The chin moms usually start cleaning themselves much more than normal.
She will do what looks like stretching exercises, labored breathing, increase in number of breaths per minute.
When it is time for the first one to be delivered she will usually stand and stretch or lay on her side and you will be able to see the contractions as she goes through the process of delivering her kits.
If all goes well, all you need to do is sit and watch.
If she has problems, you will need to know what to do.
Jo Ann