Twitching in my sleep?

These are called myoclonic jerks - they're perfectly normal and a lot of people get them. You probably do get them on your own, but you don't notice because nobody is with you to react, so you stay asleep. My partner gets them too - he jabs me in the ribs sometimes when we're falling asleep! It's not dangerous, just something some people get. I expect your girlfriend will get used to it - it used to really annoy me when I got woken up, but now it's just kind of cute :-)