I think making cookies (or something like that) would be a nice gesture that you wouldn't have to spend much money on ('cause I know a homebirth is expensive!) Or something from your garden, if you have one. But I wouldn't buy anything if I were you. Or even a nice card I guess, if you really like her. (Maybe wait till after the actual birth, to see how she does!
We are going to a birth center and I was going to make some cookies to bring, granted, I'll kind of have to make a lot for everyone, lol . . .