It’s very rare that condoms break, and many use that as an excuse when they don’t use condoms at all. Not that I’m judging you, but the morning after pill is not a form of birth control, your girlfriend needs to get on a daily contraceptive method such as birth control pills, the shot, etc... If she took the morning after pill, there’s a very small chance she could get pregnant. So you don’t have any worries.
I would also add, it sounds like in your anxiety, you lost your mind about following the instructions for Postinor dosages. You should not have forced your girlfriend (or even assisted her, if it was her idea) to take twice the recommended amount of a pill as strong as the morning-after pill. Nobody should take a double dose of morning-after pill. (Postinor 2 is not Postinor 4.) She was supposed to take one tablet as soon as possible after the undesired exposure, and then one more exactly 12 hours after the first one. If you care for her enough to have sex, you should also care about her health as much as you care for your own. See to her health now, and then encourage her to get onto a safe, regular form of birth control, such as the IUD or a standard birth-control pill. (That is, if she will ever let you near her again. If it was me, I wouldn't.) And never again let your panic cause (or assist) someone to overdose on morning-after pills.
No, she will likely not get pregnant since she took the morning after pill times 2. So, here's what she needs to know though. The way the morning after pill works is that it is a big dose of hormones. It upsets the balance so conception doesn't occur. Needs to be taken within 72 hours after the condom breaking. But after a woman takes it, all those hormones are still in their system. So, this then becomes a situation in which the body has to process the excess of hormones. Taking two won't really hurt her but her cycle will be messed up. She'll likely be irregular for at least 2 to 3 months. This may be spotting, bleeding more than usual or not bleeding at all. This is normal. She can take a pregnancy test to confirm she's not pregnant if she skips a period. But expect her period to be funky and irregular for at least 2 to 3 months. good luck and don't worry.