First, chins are not rabbits. They are not does and bucks. They are dam and sire if there are offspring. If not, they are just male and female.
Second, you'll know if she's pregnant when she has kits. Honestly, that's the absolute 100% most accurate answer anybody on here can give you. If you get an ultrasound they can check for kits that way, but it's not worth the stress on the female unless there's a problem. If you're an experienced breeder, and you're VERY careful, you can palpate in such a way as to tell if there are kits in there when they are large enough to feel. You can try monitoring her weight weekly and watch and see if it goes up, but again, this can be very stressful on a female when she's pregnant.
If I have a male and a female in breeding together, I just assume that she either is pregnant or soon to be pregnant, and I leave her alone. When I see kits, I know for sure.