She works, I guess. But most of the time Asclepius can do much better than her.

Only if you have nobody better to fill the role of healer. Her heal is quite big if you have the buffed skill up, but other than that the Guts and NP damage aren't worth using her over someone else who offers more.

Better than nothing, but Asclepius is cheaper in cost, and can do everything better than her.

The JP Asclepius even got a strengthen some years ago that allows him to gut himself. There is no point to use Irisviel for gameplay reasons. I had got her from the shop because I thought she might be useful, and didn't use her even for once.