Is it bad for a female to have multiple orgasms at a time?

Nope, multiple orgasms are not bad for you as long as you're enjoying them and you still want to keep going. Like the person above said, you're pretty lucky actually. Women's mags are always full of guides on how to have multiple orgasms and that's for good reason: not every woman is able to experience them. 

I'd just say, since you're a lesbian... make sure to take care of your partner as well. Men are biologically unable to have multiple orgasms with ejaculation, but since you're into women, I could see your partner getting frustrated if you're always up for another round and perhaps she can't.