One thing I can say right off the bat, though, is that accessing the help available to her could be highly overwhelming and/or really scary. Overwhelming because, while you can see the issues relatively clearly as an outsider, from her mind they probably seem like the biggest mess she's ever dealt with. If she's anything like me, she is probably battling thoughts that accessing help would be making a mountain out of a mole hill and roping people into supporting her when there are so many others who need it more. It's distorted thinking, but it's the way our minds work.
I'm also wondering if she might be scared of letting go of SH as a coping skill. Especially if she's been using it for years, it's probably terrifying to imagine living without it, which is sort of what accessing help might push her to do. If you think about cutting the same way you'd think about any other coping skill - running, writing, talking, painting, sports, etc. - it might make more sense. It's like, "This is how I handle hard stuff." And if that way of handling things makes them easier to cope with, then trying to live without that coping skill would be - IS - terrifying. It's like taking away a person's shield in the middle of battle. Granted, the shield is made of toxic material and slowing killing the person (it's a bad example, but you get the idea), but they feel like it's the only think keeping them safe from the swords and arrows flying around them.