Assuming she weighs more than 40kg, it’s not a significant overdose and is unlikely to do any physical harm. But still the reasons as to why she has done this need to be addressed urgently.
If she is still actively wanting to harm herself, I would suggest she needs to go to A&E, or be closely observed until she can be seen urgently by her GP.
If she is under 18, I would say you need to tell her parents what happened in order to keep her safe and ensure she gets support. If she is an adult, all you can do is support her as a friend and encourage her to seek the help that she needs.