My daughter got bit by a mosquito and her eye swelled up. i gave her some benadryl (diphenhydramine) and i kept a warm towel on it. this morning, her eye was still swollen. what should i do?

Try Ice: An additional dose of Benadryl (diphenhydramine) and ice or cool compresses should help. I would try that for 24 hours and if it is getting worse be sure to see your primary doctor. It is probably just a severe reaction to a bite but an infection could develop if it does not improve in a day or two.

Should go away : If it is a mosquito bite it should go down on its own. Maybe try cool compresses instead. Alternatively, it may not be from a mosquito bite at all. It could be a stye or even a bacterial infection of the skin (preseptal cellulitis). If it starts growing in size, i'd definitely get it checked out by your pediatrician.

Eyelid swelling: Worsening of swelling in the morning is expected because of laying flat all night while sleeping. Try cold /ice compresses, stay upright, and continue benadryl (diphenhydramine). See your pediatrician or ophthalmologist if not better.