Will my girlfriend ever have an orgasm?

Let me start this by saying that I know it's not necessary for her to have an orgasm to enjoy us having sex.

My girlfriend has never, as far as she knows, had an orgasm. She doesn't play with herself at all and hasn't ever been close while having sex. Recently she's said that she feels like she's getting pretty close when I go down on her but just as it's getting really good she gets the urge to laugh and I'm asked to stop because it feels too ticklish to feel good anymore.

Is this normal? Is there anything she or I should try and do differently that might push her over the edge?