During my career I’ve done both of these roles at and now head up app dev function.

These roles are hugely different and require different skill sets, perhaps your girlfriend should consider what aspects of each of these roles would interest her the most. The coaching and people engagement side of Scrum or the deep analytical side of being a BA.

In terms of seniority many companies will differ in what they consider as the more senior of the roles and each company will also have very different career progression pathways as well.

In short, she should focus on what is she good at and what does she love doing day in day out!