My friend is not taking her medication and it's really upsetting me.
Is she required to take this medication daily?
Yes, she needs to take this medication to prevent her from getting sick again.
It's good that you have concern for her and her health. It's a tricky situation because she should be able to make her own decisions. But if it's something that puts her health at risk you may need to intervene.
I just don't want to sound like a jerk but my friend really needs to take their medicine.
I would recommend approaching the situation in a calm manner. Having a discussion with her that you are concerned for her health and that you care for her may give her the inspiration to start taking her medication again.