She might have been a loner. There's not really enough information to decide that. A loner is someone who prefers to do everything alone. Not joining clubs is not enough to classify someone as a loner.
I don't think you could necessarily say she was a non-conformist either, since there are even clubs for non-conformists, and she wouldn't have joined that!
No, it just means she prefers to set her own agenda.
Interested in Language