A thought has occurred to me regarding how Rebeca's temperature powers work, and I'd like to clarify some things for future reference.
In the current situation, Rebeca's temperature is rising on account of her mounting frustration with what's going on, and this is noticeable. However, you would really only notice it if you were basically standing right next her. In her normal state Rebeca's skin would feel like she has a very high fever, and if it was raining you'd see steam coming off her due to the water droplets evaporating. I've seen this same thing happen to bald people in real life, their heads start steaming because your head is one of the warmest parts of your body due to all the blood flow to your brain. Her temperature does fluctuate in response to her emotional state, but in much the same way that a regular human's does; you get a little hotter when you're angry because your body is preparing itself for a fight or flight scenario, and when you're depressed your temperature drops, for reasons that I can't recall at the moment. Additionally, the human body's core temperature naturally fluctuates over the course of the day as it self-regulates relative to its environment, usually only by a couple of degrees unless something is going very wrong. Rebeca just has a naturally higher starting point and her range of variation from that point is a little wider.
There are two situations in which Rebeca's body naturally experiences a drastic change in temperature.
The first is when she's physically exerting herself. For example, if you were to walk into a gym either during or after she's been training or fighting for a while, it would feel like you just walked into a sauna or steam room. Touching her would hurt if you held onto her for a while, but it wouldn't be much worse than a first degree burn. Otherwise, her environment would be basically intact, just uncomfortably warm for anyone other than her. Obviously the smaller the space, the faster it warms up and the more uncomfortable it would be.
The second is when she's actually using her flame powers. Her use of these powers is basically the same as the way you use your limbs; mostly they are under her conscious control, but sometimes (usually when she's extremely agitated) she uses them out of reflex. That's when things get all burny and melty around her, and she winds up naked. If you've ever been pissed enough to want to punch something, and then actually did it, that's the condition that Rebeca has to be in for accidents to occur. It is a state she doesn't reach very often, because A. she believes that most things aren't worth getting all worked up for (though she's still human, and her self-control has limits, she just usually leaves before then), and B. she's very much aware of what happens when she DOES lose her temper. Even in battle, she doesn't often use her flame powers unless she feels that it's necessary.
For the current situation, if you were standing close to her you would feel that the air is noticeably warmer, though still well within tolerable ranges, like if your were holding your hand next to a room heater or central heating vent while the furnace is running. If you were paying very close attention, you would see heat waves coming out of her mouth and nose as she breathed. She's safe to touch, she just probably won't let you. The burning of the foam is a result of its chemicals reacting to extended exposure to her higher temperatures. As a reminder, she has a Kabuto clinging to her chest underneath her shirt who is just now getting uncomfortable with how warm her host is getting.
I just dropped some SCIENCE! on ya'll! *drops the mic and walks away*