Originally Posted by
yogaflame
Moira was only introduced in the Claremont era, so she never interacted with the O5 during their original run, but later stories have made it so that she was closely involved with Charles's operations, even though they had become estranged(romantically) for more than a decade by the time he was starting to form the team(Amelia Voght was his girlfriend at the time, also a later retcon, and largely forgotten in post-Lobdell canon).
However, in Claremont's run she was fairly close with the new team(first appearing undercover as a 'maid' before busting out a machine gun against that demon), particularly Banshee of course, but she also employed Lorna, Madrox, and Jean at various times at her Muir Island Research Center, not to mention is the legal guardian/adopted mother of Rahne, and had close contact with Kitty, Colossus, and Nightcrawler after their Mutant Massacre injuries, and later Excalibur at large.
It was also revealed that she tampered with Magneto's DNA when he was under her care after having been reverted to a baby at the end of the Silver Age(though it is also revealed that her tampering was essentially undone by the use of his powers, so he was still acting under his own free will for the most part). She worked with Beast and Charles extensively on the Legacy Virus, which she herself contracted eventually, and it was her research that enabled a cure to be found(after her death at the hands of Mystique).
She has been sorely missed in this modern era, with almost no human ally characters of note appearing. It will be interesting to see how Hickman resurrects her, though, as her death was quite definitive, and happen so long ago.