HELP!! my 8 year old sister fells bad, PLEASE read.?

I'm on my computer and my 8 year old sister tells me that she fells like she has a headache so i thought well maybe you are getting cold because on friday she went swimming. so i told her to go get me the thermometer so i could see if she has fever i put it under her arm and a few min later it started bepping so i took it out from under her arm and had ( 95.5'F) her normal tempature is 97.2 its was about 8 min ago is when i checked her tempature she layed down about 5 min ago and now she is asleep. WHAT DO I DO, our parents are asleep. do i just let her sleep until the morning and tell my mom. i'm kinda scared because of her body tempature being low 95.5f her normal body tempature is 97.2. i'm 14 and ive always watched my mom when she has to give my sister medacine for a cold because i might be babysitting her and she have to have some medacine. WHAT DO I DO? does she need some motrine?