You can order a test kit to have her pregnancy tested. It's not expensive and there are instructions how to collect the sample.
http://www.biotracking.com/
There's a possibility that you're not getting Bess's full capacity. When you hear those big numbers for milk production, they're for a cow with no calf, extra supplements, twice a day milking, and possibly hormone treatment.
Bess's failure to catch might not be her problem. It could be the bull's problem or the possibility that his visit wasn't timed with her cycle. She's only receptive for a few hours each cycle.
Nubians are good milking goats, with some of the best tasting goats' milk, but it doesn't taste like cows' milk. Your family may not be willing to switch.
You can try a different bull or wait a while to see if her calf settles her in a month or so. He's old enough now for some breeds to be fertile.
You can wean him now to see how much more milk you can get from her.
You can also experiment with extra feed to see how it affects her milk output.
What breed is she? How big is she? Are all her quarters sound and do they all give the same amount? Do you strip her every time you milk her? Do you milk her once or twice a day? Where is the cream line in her milk after 24 hours? How good are your pastures? Are you still feeding hay? Where are you located?
If one or more of those questions shows something that is a problem, then another cow may not perform a whole lot better in the same situation.
A cow in the lush pastures of North Carolina can easily outperform a cow in the barren fields of New Mexico.
Milk is never free. We pay for it with the effort we put into it and sometimes with the feed we provide the cow.
