No, you can get this pill at target. You don't need a prescription.
There's no telling exactly how it will effect her, some women experience heavy bleeding for a short time and some women just get spotting for awhile-- it could even be just like her regular period... it seems like a small detail to me when you are trying to prevent pregnancy.
The pill needs to be taken within the first 72 hours of sex, but you can take it within 120 hours. The sooner you take it, the more chance you have of it working so don't put it off until the last minute if you do decide on taking it.
Is she worried about pregnancy?