well... it's difficult to say. some of them don't really do all that much! snoozing and getting excited about the bath is sometimes what they're like! how long have you had her for? sometimes, especially if they've come from a bad situation, it takes them quite a while to get used to the new environment, new people, new routine. does she explore the surroundings when she's running around? what's her cage like? how does she respond to chews? does she have a house/tunnel/hammocks she can hide in? you said in your previous post that she was in a very small cage before. it's possible she stays in one place because that's all she was able to do before. mind you, all mine have a favourite spot where they spend most of their time.
it's not a good idea to let the girl and the boy play together. keeping a close eye doesn't quite help - by the time you notice something fishy's going on, it's too late. only takes seconds to get her pregnant. on top of that, you can't just put two chinchillas together to have a play. they need to be introduced gradually (some people use methods that take less time) and they are fully capable of killing one another so if they don't like each other... chinchillas bond with mates so when doing intros, you really want them to live together once they bond rather than have playdates.
i have never purposefully bred so maybe the breeders on here will have a better answer but i don't think there are tests for suitability for breeding. the general rules are: you need to know the history of the animal and the pedigree for five generations (malocclusion for example is a genetic disease but may skip a generation so your animal may be sound but the genetic background is flawed in which case the babies may be sick - malocclusion is a rather cruel disease, there are other genetic problems as well), the breeding pair should be healthy and of good weight, compatible colours, be over certain age (this is later for certain colours)
as jamie said, you have no idea about the girl's history, she came from a bad situation and she doesn't seem exactly happy either. having kits could kill her. i would absolutely not breed from her.
if you really do want to have kits, it would be best if you got a breeding pair with full pedigree. you will need a chinchilla experienced vet who has 24 hour emergency cover and is confident doing emergency c-sections etc. you'll have to be prepared for complications and the possibility of kits and/or mum dying. you'll have to think in terms of numbers and time frame, chinchillas often have triplets and quads (these will need your help with either rotating or hand feeding), they're pregnant for 111 days and go into oestrus within 24 hours after giving birth and about once a month when not pregnant. they have two horned womb which means they can get pregnant at different times, the babies are usually delivered at the same time and the younger don't survive. chinchillas can live to quite an old age and they can get pregnant and give birth at quite an old age (i think i heard somebody had a 17 year old with litter) so you'll have to think if you'll be wanting to do this in 17 years time still. sometimes when they have to do a c-section, they spay the chinchilla at the same time to reduce bleeding - this would mean no more babies but perhaps mum would survive.
when it goes well and there are no problems, it's lovely. if something goes wrong, it's extremely hard work and heartbreaking. when fluffy had mastitis and we had to hand feed, every time i went into their room, i was terrified i'd only see two of the babies moving. thankfully they all pulled through but i would have been absolutely heartbroken if i had lost any.
