I seem to remember years ago some people listing their pronouns by she/her/hers. I think she/her, she/they, he/him, etc. is just a shortening of listing all three while also being inclusive. As you mentioned some individuals are more fluid and may go by she and they but prefer she so it is listed as she/they.
I know cloudflare has a free tier and allows you to put rules like this in place. AFAIK you’d have to use them as DNS at least in order to use this feature. I use Cloudflare tunnels and access to facilitate remote access to my home-server, and I know I have this same rule in place.