I don't know anyone in Irvine either...

If it were me. I'd put him in my bathroom. If she has three kitties already, how will her manager know she has that other one if she keeps him in the bathroom when she's not home - so he wont be in a window??????

She loves him, we can see that. I don't even have places for MY own cats, so advice and prayers are all I can spare.

IF IT WERE ME: take kitty in, put in bathroom until other 3 get to know him. Then, she has 4 kitties. If she has to, cover the windows while she's at work so there wont be 4 kitty heads looking out her windows. She's already done so much - the vetting, supplies, falling in love and having it be utterly mutual - they should be together.