The *result* may be repeated contentious behavior, but I wouldn't call it "habitual". Is she contentious about anything other than rules? If she argues about *everything*, then I'd see your point.
If she honestly has problems keeping rules straight in her head, the GM would deal with that differently than, "This person is just habitually argumentative." And, honestly, if they've been switching between multiple d20 games, one can hardly blame her. Even the best of us can lose track of which rule applies in Pathfinder, which in 3e, and such.
Far more likely, it's not the group that's been changing rules, she's been changing what games she's been playing in. This groups is likely to have picked her up online, and has not been playing with her for 20 years or something.
clues:
A) the OP said they'd only changed rulesets a few times
b) the OP is discussing things over FB, not in person or on phone
c) the OP said she's played a long list of d20 games
It is probable she spent the most time in 3.x (based on example argument) and thus the other d20 games' differences trigger her to cite 3.x rules (that she knows) when she hits rules she doesn't understand.
One possible reason for the arguing is that some people question or argue about things when they are out of their element. I've seen it in project meetings. The guy who is in over his head will not only ask a lot of questions, he'll challenge certain points and bring up "why don't we do it this other way" discussions that side-track the meeting. Now initially, it'll seem OK. You should ask questions when you don't understand something. But the problem is that a guy on the team to build a bridge from NY to NJ is supposed to know how to build bridges in general and understand that it's important to build one from NY to NJ. When you get a guy who is supposed to be those things, it is disruptive to progress when every meeting is bogged down in challenges over "does it have to be a bridge?"
So part of the OP's problem might be that they are trying to play 5E (or whatever), and the problem player is only prepared to play 3.xE. I seriously doubt she's read the rules, dug into it as everybody else has.
Another consideration is that some people have piss poor memories. I have had work conversations with people and 2 weeks later, when I check on the progress, they have no recollection of what I'm even talking about. Not just forgot to do it, they won't remember that we talked, they won't even vaguely recall the subject of moving the MacGuffins from the old closet to the new one. They'll ask "what's a MacGuffin?"
Drives me nuts. Lack of memory makes people look stupid. Asimov wrote a short story about how a memory enhancer made a "dull" man appear to be sharp. It's a valid observation. Some people can't remember any darn thing, and it shows up when they do stuff like play a game that they don't ever remember the rules to.