WHOAaaaaa Casanova, it is not a "psychological thing."
She can pee all she wants before good sex, but that won't make a dang bit of difference.
For the love of God, the worst thing she should do is ignore it!
But you're right, she won't pee.
However, if she relaxes and lets it happen, she will experience the most explosive orgasm. The "peeing sensation" is commonly referred to as 'squirting'. Otherwise known as, 'female ejaculation'.
Most men and women love when his/her partner squirts.
I wasn't able to give in to it until I was in my late 20's.
It's an indescribable sensation, but unless she is 110% comfortable, trusting, and relaxed, it won't happen.
Be patient with her and please tell her that it is absolutely normal. It's an idea that she has to be at peace with, and when that happens, she's going to be blessed with the ability to have the most unbeleivable orgasms.
My advice from here,



GO PRACTICE!