My daughter (18 years old) right leg occasionally gave way causing her to fall. what are the causes and remedies to help? thank you.

Could be knee problm: If no medical issues / trauma history otherwise, intermittent give-way of leg can sometimes be due to meniscus or other ligament issue in knee. If pain better localizes "starting" or trouble spot, then needs seen to address that, but otherwise, would suggest she see an orthopedist for history / exam / likely MRI and possible arthroscopy.