Yep, that's exactly the treatment for an ovarian cyst. Most of them will typically burst on their own and the initial pain is staggering. All you can do is take pain meds if they're offered and wait it out. The body is more than capable of absorbing the fluid so there's nothing to worry about there. She'll probably feel uncomfortable and bloated for a few days. It's just one of those things you have to grit your teeth and remind yourself that it WILL get better sooner rather than later.
There are more than one flavor of ovarian cysts and some are more cause for concern than the usual ones that occur due to what I think of as a misfired egg. I've had plenty of those along with hemorrhagic and chocolate cysts from endometriosis. Those tend to not rupture on their own and surgery usually is only considered after the size has been tracked for a few months and it gets so large that it causes more symptoms or interferes with fertility. Ain't it great to be a woman?! :-/
Yes this is appropriate for ovarian cyst treatment. She may have some bloating like a period and even carmping for a couple of days.
Cysts are eggs that form and don't release. They are ususally recurrent, often cause pain then rupture on their own. Common treatment is birth control pills which stops ovulation. See a GYN so you can avoid the ER next time.