Right, if you haven't seen her yet, here is a script. I'd recommend seeing her in person if possible, as avoiding face-to-face contact is the sort of thing people sometimes do when they're scared of being caught out - obviously it would not be true in your case, but I think people who work in education sometimes see shirking when it isn't there.
'Hi personal tutor, please can I speak to you privately later? It's a bit urgent, I'm afraid. I will be here until 'whatever time'.' (you can email this bit)
Then turn up, get ushered in, sit down.
'I'm afraid that I will not be able to come to uni on Monday as I am due to attend a Women's Aid appointment. I have spent the past several years in a relationship with I have realised, due to recent incidents, is abusive, both emotionally and physically.
I know it sounds strange that I've just realised the physical part, but I'd just become so accustomed to it that I only realised when speaking to a friend (that's us :)) just how bad it was.
I'm now trying to leave, really trying, and he's not taking it well. He texts me very frequently, he emails, he calls. I'm finding it quite hard to cope with, in addition to life in general (DS, uni etc) and so I've been put in touch with WA for help.
My appointment is on Monday. I hope it's ok with you for me to go. I'm really sorry about the timing but I don't think this can wait.'
You could even print this (or something like it) off, then hand it to her and watch her read it. The important thing is that you're there. Your body language will be far more convincing than any words. I can't imagine she will cause any difficulties - no-one hearing that story could.
I hope I haven't overstepped and that this is helpful xxx