Several things come to mind. Sometimes cats can sense when someone is ill. Has she seen a doc recently to make sure all is OK? Any pains she's been writing off as "it's just [fill-in-the-blank]"????
Don't mean to pry, but do you live together? Does she have her own kitty? Perhaps she smells like a strange pet - a kitty, a dog.... something the cat doesn't like?
Has she tried changing the scents she uses? Soap? Shampoo? Fragrance? If she uses one thing all the time, just try giving it a change and see if there's any change in his reaction. If it's not a scent, then here's what we'd do.
We've found that our cats prefer to head over to the people who ignore them, rather than to someone trying to give them attention. Give it to a cat to go pick out the "I'm not really into cats" person.
I'd suggest you completely change tack. Cats are contrarians (for the most part). When we feel like loving on our kitties and they're not cuddly, we start ignoring them. This works.
So I'd suggest she begin ignoring him altogether. She should act like she doesn't even know he's there. Suggest she not even look at him.
In the meantime, do things to help him come to associate her scent with "good" things. This is a "trick" we use to help socialize cats to each other, but it's worked with cats who don't like certain people. (For instance, a cat that was abused by a man who now does not like men.... ). Have her take a couple of t-shirts she doesn't want back and get them really good and sweaty. Put one under his food dish and leave it there (if he free feeds - otherwise, put it under his food dish when you feed him). Put one in his favorite bed. YOU play with him - and when you're done, put treats down for him on one of her sweaty t-shirts.
Just wait for him to make up his own mind. The more she tries, the more he'll resist. My guess is that after a couple of weeks of this - maybe a month - he'll relax around her, and maybe even headbump her himself. This is a "trick" we use in socializing feral kitties. Just be in the room with them, ignoring them, never looking at them (this is seen as a sign of aggression) - look at their forehead or over the top of their heads. Don't reach out to them (unless it's with a spoon in your hand with some gerber's chicken babyfood in it) - never directly face them, spend as much time as you can down at their level - doing other things and completely ignoring them. Wait until they get curious enough to come to you. And when they do? Don't react. Don't reach out to pet. Let them check you out. It can be really hard and very challenging - but it is worth it, and I think it might work here. When they've got that trust thing down, they'll bump you, or rub up against your leg and turn their butt to you. That's when you first pet them. And you sit down, at their level, and slowly reach out, palm down (palm up is also a no-no), for that first pet. Now this last stuff may be extreme in this instance. But the idea is - she should ignore him while he has time to come to associate her scent with good things, and she should stop pursuing him, just wait until he comes to her.
I think she should approach it like he's just scared of her for whatever reason, and while you work on getting him to associate her scent with good things, she should treat him like we would when socializing a feral kitty.