I personally would question why you are breeding from a goat with a known problem in a weight bearing joint that is most likely to get worse with the additional weight and possibly also due to hormonal changes during pregnancy, but....
After you have ruled out CAE (blood test asap) - she may well have had joint ill as a kid (the breeder would have known!) She will need ongoing pain management, and as such NSAID's (like Flunixin or Metacam) are probably your best choice. They are safe during pregnancy, and probably safer than some of the herbal treatments, which have never been tested on pregnant animals.
If she turns out to be heavy milker you will have further ongoing problems, as all these painkillers have significant milk withdrawal periods, and I would be reluctant to feed milk contaminated with pain killers from her to the kids.