Your friend here could be referring to three different things when she says that she is “Reformed” Catholic
The first thing she could be referring to is that she is a member of any one of the Independent Catholic denominations like the Old Catholic Church, or the National Polish Catholic Church etc. Many Independent Catholic Churches use the term “Reformed” Catholic as a synonymy for Independent Catholic Churches. These denominations aren’t Protestants they are still in the Catholic tradition, just not in communion with Rome.
She could also be referring to the Reformed Catholic denomination that is in Venezuela. Formed by Anglican and Catholic clergy. It is apart of the Orthodox Anglican Communion. (It’s not apart of the Anglican Communion, which is the biggest Anglican denomination.) So it is a branch in a Anglican denomination, so it’s Protestant. But if she doesn’t live in Venezuela, then this is no longer a possibility.
A third and final thing she could be referring to is the Reformed Catholic denomination that is based word wide and is not the same one as the one in Venezuela. Formed 1879, some priests who left the Catholic Church formed a few congregations, chiefly in New York, and began evangelistic work on a Protestant basis of belief. So this too is a Protestant denomination.
The most likely possibility is probably a denomination in one of the Independent Catholic Churches, sense this is the biggest. If she’s not in Venezuela, like I said, the second possibility is no longer possible. And she is probably not the third possibility since they are extremely small with less then 5,000 members, but there is still some possibility to that third one.
(Sometimes in the Anglican Communion, the biggest Anglican/Protestant denomination, some members might refer to themselves as “Reformed Catholic” but this is not a widely used synonym so it’s probably not this one but maybe.)