People who use "mixed" pronouns like that (She/They or He/They) are often people who grew up being called she or he and don't object to it, are used to it, but it's not entirely inline with the way they see themselves. Or they're in transition. They would like to at some point go by "they" but they're not there yet in their life for whatever reason. Sometimes it's easing friends and family into it, sometimes it's folks grappling with their identity.

This is what I've seen from the folks I know who use mixed pronouns.