My Daughter Has A Bite On Her Arm. Is It A Harmless Bite Or Should I Worry About Her Arm Falling Apart? Any Ideas As To What It Was That Bit Her? Should I Panic?

It's red and swollen and now showing bruising around the outside. She says doesn't hurt but it itches. No fever. No vomiting. Loss of appetite. Whiny and irritable, more so than usual. But then she is four. This is day two. The first day thought it was no problem just a small bite. Now i am starting to get worried. Then i looked up some pics of spider bites and I'm freakin out.