Back in the summer of 2019, Rose had to have emergency surgery due to herniated discs in her spine that threatened to paralyze her. The injury was sustained at some point during the filming of Batwoman‘s first season, and over time as Rose began to experience numbness in her extremities, realization set in that the injury might be much more serious than at first believed. She didn’t reveal this fact until that September, well after the surgery, and as far as anyone is publicly aware, she has indeed recovered just fine from her injury. Variety reports an anonymous source that claims Rose departing the role has nothing to do with her health, but it’s difficult to say exactly what that means.
She probably is perfectly healthy now, since doctors intervened before the injury could become permanent, but it may have affected her strength and flexibility in a way that couldn’t be recovered in time for filming, or perhaps the long-term viability for whatever reparative measures were taken in surgery, either tissue or medical hardware, are a factor. It’s not necessarily that she’s unhealthy, but there could be uncertainty enough around how safe it is to continue working such a stunt-heavy role after a spine injury, even a healed one, because of increased risk. It’s also entirely possible that the injury has simply brought Rose to second-guess her dedication to the role. Anyone would question how willing they are to continue working anywhere after getting so seriously hurt on-site, even when there’s no one at fault.