since one or two versions ago she became recruitable after you save her.
in OP case, he is talking of the bug:
to recruit Iris, he needs to talk with Ayda to get a cheat potion, but if you have recruited her, there is no one to talk with and you cant pass Iris chalenge without the potion. So it becomes impossible to recruit her.
I think she goes back to Gorn after you recruit Melissa or kill her brother, so it should still be possible to recruit Iris after finishing main quest.
To fix it, dev may allow to talk to Ayda inside the mansion or let her assistant handle it in gorn.