What could a warm to touch, that has become swollen, on the right arm be?

I would definitely get medical attention TODAY. Could be a few different things...but first that comes to mind is a cellulitis. The fact that it has progressed overnight has me very concerned. If it is cellulitis, it can be treated with antibiotics, IV if the physicians think it is serious, with probably a course of home antibiotics later. The yellowish color...could be a bug bite reaction...but honestly, without knowing medicine and actually seeing her, it's difficult to tell.

Go pick her up and get her attention now...if it has progressed this much overnight, you do not want it progressing any further.

Yes. If you can call a doctor, he may help, you might try a pharmacist for treatment.

But ultimately, you need to be prepared to go to the emergency room before Noon to get it taken care of... it is getting worse, not better, and it could be a poisonous insect bite, which doesn't have to hurt, but causes increasing damage.

yes, see a doctor. Any abnormal swelling or heat may indicate an infection. Just because it doesn't hurt doesn't mean it should be ignored. It could be a bug bite or an infection. Call your doctor and ask if she should be seen. Chances are the doctor will ask you to come in right away.

I think it is some kind of bug bite or bee sting. Take some IB profren and call the doc just to be on the safe side.

Seek medical attention right away. This is not something to wait around with.

Get her Emergency Treatment NOW!

Sounds like she has an infection

Get her in to the dr. Sounds like a venomous spider bite. Don't mess arond with it.

Yes, now! It maybe and infection/allergic from a bug bite or sting. Or one of many other infections.