Given the redness
and swelling of the lips, this could be a case of vulvo vagintis.
Kindly get a urine routine test done for your child to ascertain the source of infection.
Ensure that your child does not scratch the affected part and keeps the hands clean. Proper washing of the affected area is very important.
If there is any whitish or curdy discharge, it could be a fungal infection
and an anti fungal might be indicated.
If the condition is becoming worse, dont wait for 48 hours. Kindly get her seen by a lady Gynecologist as she would be definitely more comfortable in her presence.