I think (at least in my experience) that here in England it is still very much a boys' name, probably due to association with the male chef
Ainsley Harriott.
I find it trendy even for boys so it's extremely trendy IMO for a girl. Aside from that it's not very attractive sounding for a girl in the way that
Ashley does though I prefer to see that as well as
Ainsley on a boy.
It's certainly nothing special.