I literally just bought this ryorifrom someone to breed with one I've had for a while. However, when I go to the breeding grounds and try to select a female, there are no options in the drop down. I tried naming her, but it still doesn't show up, even after refreshing the page. I also tried opening the page on my phone and it still didn't pop up.

I don't play often, so I'm not sure if there's some mechanic I'm missing, or if this is legitimately broken. My friend who plays more told me to come here.

The girl you bought is infertile, which means she can't breed and is irreversible. (That's what the pink heart with a red circle and line through it means)
I would guess its likely because of the high stats she has, so the owner likely felt uncomfortable letting her go fertile, and used the infinite kit you can get from the diamond shop.

Interesting, thank you for letting me know!