Thanks for writing to health care magic.
Your daughter is having pyoderma
It is a bacterial infection.It is red and tender initially,then becomes yellow and finally pus drains out.
You can ask her to apply a topical antiboitic cream like t bact and take oral pain killers.Hot fomentation will also help.
Ask her to use loose shirts.Keep the area dry and clean.Remove underarm hairs Regularly.
You need not to rush to emergency room.
Hope this will help you.Take care.