She is 25. I have explained to her lots of times what is happening what will happen the feelings she will experience, if she feels like she needs to pee it isnt pee (as long as shes peed before hand) etc
That 'need to pee' feeling is not necessary for an orgasm. That feeling is associated with 'squirting' or female ejaculation, and does not accompany all orgasms for all women.
Different women orgasm in different ways, and orgasm is accompanied by different feelings in different women. For instance, some women find that they need to relax their vaginal muscles when they're getting close to orgasm, whilst others need to push themselves over the edge physically as well as mentally (RawDog or SG83 might remember the thread we discussed this in. I can't remember which it was).
If your girlfriend knows what way works for her when she's alone, it will make it easier for her to orgasm when you are together. Does she even orgasm when she's alone? She may never have had an orgasm before at all and could be too shy to tell you.
She says she can't help it and suggested I tie her up to stop her moving. Is this really the best way to get past it?
It might just work. And maybe she has a strong sub streak and doesn't feel right orgasming unless you 'make' her. If you both feel comfortable doing this, there's no reason you shouldn't do it. Just make sure you have a safeword.
Is it normal? Is it really that hard for herself to cope with mind over matter to go 'over the top' ?
Not being able to orgasm at all is quite normal, let alone doing so with another or during penetration. In fact there are some women who prefer NOT to orgasm during sex.
If I tie her up and go down on her how do I know I need to keep going if she tells me to stop but its just caused by nerves?
Use a safeword that can't be used 'accidentally'. If she asks you to stop using that safeword, she really means it and you should stop.
She says when she rubs her clit alot she chaffs and has to stop which makes the feeling go away. I asked her why doesn't she just use lube or rub it in a different way or place but she just ignored me.
I've rubbed my clit so hard that it hurt and I had to stop. I've also rubbed it so hard that it hurt, but I didn't give a fuck because it felt so good and I've kept going anyway. Lube would be a bad thing for me because I really need the friction for it to feel good. This may, or may not, be the case with your girlfriend.
She may have ignored you when you asked about it because she's embarrassed to discuss something so personal with you, or she may not even know the answer herself.
She confuses me, is she embarrased or simply not know what to do or genuinely scared?
No idea. You need to ask her that. It would probably help a lot if you stopped putting so much pressure on her to orgasm. Some women just don't orgasm easily. If she is one of these then the pressure you are putting on her will be making her feel bad. Just relax and let it happen when (and if) it happens.
I'm pretty scared if it was past abuse, I would have no idea how to get her to go to a councellor I don't think she would want to. And I think it would take a long time to help her. She is sometimes a bit shy but she definitely doesn't seem to have trouble letting go. She was peeing on the toilet when we were in the bathroom the other day and started taking a dump and wasn't bothered I was there!
I'm puzzled
It could be to do with past abuse, but that's not necessarily the case.