I don't know of a holster maker who doesn't make something for the PM9. The real problem is, what will she find comfortable after 6 weeks of daily carry? That's why so many gunnies have a closet full of holsters that just weren't exactly right.
How's she gonna carry? Many pro women shooters carry cross draw. IWB on the female hip bone structure is completely different (Thank you, God!) I would recommend you get input from women shooters only to sort out the actuals on what is right. Mas Ayoob's books on Concealed Carry and Combative Handgunnery address this as a completely separate part of their holster section because the ergonomics are signficantly different.
Case in point, most women can reach around and touch their shoulder blade, men usually can't. It means they work with shoulder holsters to a much better degree than we do. They will also CCW with a jacket or sweater sooner in the fall, or at least can, because of other physiological differences.
She also has other carry options than only a few men would bother with - purses, fanny packs, etc. So, for an important part of carry, and one she needs complete familiarity and confidence with, study up. It's not about what works for the guys.