My dr. also took me off my meds when I was pregnant. I actually do better when Im preg. I get hypomanic right after I have the baby, but I breastfeed so I still don't go back on meds right away.
I think there are meds that can be taken during pregnancy, but nothing is a sure safe bet, and I would assume they take us off the meds and try that first, only using meds in pregnancy if absolutely necessary. I've talked to other women with bp who've said they felt at their best in pregnancy as well.
Take Care and congrats to your sister
Good judgement comes from experience and alot of that comes from bad judgement.