For some reason, it sounds like waxing is important to you. If that's the case, why commit to someone who doesn't?
Honestly, as a woman, unless she is open to trying things, I don't think there is a good way to phrase it, my husband has tried and no matter how he worded it, it always pissed me off, or got me irritated. Waxing might be out of her comfort level and you just need to learn to respect that.
It's the way you ask her. I like Grim's approach. Waxing is asking a bit much I think...shaving is quicker and doesn't hurt. I have a sugaring (form of waxing) recipe. It doesn't hurt as much as normal wax. Contact me if you're interested.
There is no way that I can believe her arm hair would bother you that much. If she is that hairy down there (I doubt it I think your a idiot and need somebody else) after you go down on her make it obvious you have pubic hair in your mouth and spend time getting it out. That will get her to at least trim it. I can see her maybe being that bad down there but her arm hair? come on
i'd say, the only legit reason to ask her to maintain her pubes is because you are having trouble performing oral on her. if this is the case, say something like "it would be easier for me to please you if..." however, if the reason for you wanting her to maintain her pubes (and arm hair for that matter, which makes me think this is the case) is bc you are a shallow jerk, then grow the hell up or find another girl.