I use to be on the shot depo and had unprotectedsex for 3 years while i was on it before i stopped taking it a couple years ago. You only get the shot once every three months and it stopped my bleeding too
Just so you know, my best friend was on birth control and she took it regularly and didnt miss a dose. Her and her bf started a month later not using protection. A month later she found out she was pregnant. Just be careful
I would use protection until she can take her pill more consistently for a couple months. Suggest a cell phone alarm and keeping her pills with her so she takes the pill at the same time daily without fail.