Is my girlfriend weird for behaving like this?

Dude it's perfectly normal. Me and my girlfriend have been dating forever, and she still insists on paying me back for some stuff like that. It's just her personality, she felt like she owed me, and she gave it back to make herself feel a little ease in her mind. It's normal. And as far as the marriage thing goes, I'd say you're the one acting weird. If you really love her, and she loves you, why would you insist on the marriage.? Are you feeling insecure, and wanting to marry her just so you can feel safer about not losing her.? Just relax man, she asked you for some time, give it to her. Just go with the flow, and everything will work out eventually... ;)