lol and other abbreviations, along with smileys, slang, and sentence length are the text equivalent of body language. They're slightly different with everyone, but the general premise is the same.
As far as lol goes, in my experience it's basically the text equivalent of smiling. It's a way to show your positive energy. And it's so easy to do that most people don't even think about it. It never really means that she's literally laughing out loud.
The best way to deal with a girl who says lol a lot, or really any girl you're texting, is to mirror their texting style. If they say lol, throw in some more lols in your texts. If you have some personal vendetta against lol, typing out "haha" does the same thing. Same goes for smileys and sentence length (fun fact: I use smiley's all the time, it keeps messages from being misinterpreted...mos t of the time). Mirroring like that builds a subconscious connection between you two, makes her feel like you're like her and relate to her.