Fiancée was put on leave to get psychological problems sorted out, but wasn’t allowed to come back due to employer hiring someone else during her leave. Is there anything we can do?

I’m pretty sure promising someone a position back after being on leave but then hiring someone else is illegal or something. We’re both unemployed and struggling, and the job that she briefly had was a really good fit. This all happened in January so hopefully that’s not too long ago for us to be able to get help. Any advice would be appreciated! Thanks y’all. Also, we have text conversations proving that all this bs happened, if that would be of any help.