My friend was bitten by a spider or something in her finger,4 days ago,and has swelling and pain .?

It started in her finger and is now traveling up her arm,about midway now.She claims it is very painful,and can barely move her arm.We live in Michigan,what on earth could have caused this?She is not running a fever,and feels fine except for her arm.You can actually see the redness go up her arm.SHE FLAT OUT REFUSES TO GO TO A DOCTOR,so I guess we just want to know what could have bitten her.