To my knowledge, it is common for she/they to mean "either she/her/hers or they/them/theirs is fine".
If a person tells you that they prefer one or the other, want you to use both in a rolling fashion, or some other specific arrangement like "he/them/his" then you should respect it, but in my experience that isn't normally expected just from saying "she/they" or "he/they".
It's also the case that some people use he/they or she/they because they want to go by she or he but aren't confident in their presentation and so they kind of give people an "out" by having they in there (not saying this is everyone, just that I've known a couple people like that). If you get that impression it might color your choice of what pronoun to pick, but its not really on you to suss that out