So sorry your babe is sick!
I agree with several PPs that breastmilk is absolutely the best thing. When we need to rehydrate someone around here, we use Smart Water. It has electrolytes, but has no flavor and tastes only like water. We sometimes make ginger tea with it for pukey kids. The reason I mention it is, your babe might accept it in a dropper, a little at a time, where she'd scream if you moved her from the breast after a short time. Might help, can't hurt.
Oh, and if she's vomiting immediately after she stops nursing but she's been nursing for awhile, remember that she's had several minutes (or however long she's been at the breast) to digest and absorb the milk she took in right at first, so it's definitely not a waste to just let her nurse and puke, nurse and puke, unpleasant though that may be. (Well, OK, so this was always my personal assessment of this particular situation when my kids were little; maybe I made it all up!) At least BM won't burn up her thoat!
Does she still have tears when she cries?