Does she really have a right to be upset?

My boyfriend and I have a 2 bedroom apartment together. We weren't utilizing our second room for anything except storage, so we let one of our best friends move in. Not too long after moving in, he started seeing this girl. She's pretty nice, I don't have any problems with her, except she invited herself to move in. She's not on the lease (and doesn't want to be, seeing as her and my roomie have only been together for a couple of months), but she treats the place as if its her own. She's runs the washer/dryer at LEAST once a day, and leaves the AC running all day long while my boyfriend and I are at work, even when we ask her not to. Our new electricity bill is over $100, which is super high for us cuz its normally in the $40-$50 range. That, and they don't grocery shop for the house, we do. They shop for themselves, and still eat our food. Were spending tons of money on this girl.

So today, we asked her to start paying rent next month. Everything would then be split 4 ways, and be much cheaper. She threw a fit and started yelling, saying she shouldn't have to pay because she has "so many bills" (even though she just spent $200-some at the mall the other day, but that's none of my business) and she doesn't know why we're asking for rent now, and that we must be greedy. She said she'll be moving out, but still. I don't care where her money comes from or goes to, the point is, is she's boosting all of our bills by a lot. My boyfriend and I barely have any money left over after bills anymore.

Should she really be as mad as she is? I feel like WE should be the ones who are pissed off.