Rhue continued working until 1996. So it's safe to assume she would have been perfectly able to do would have probably been only a couple of days of shooting.
So if the real reason Harvey chose not to use her was just because she was in a wheelchair--now that is disrespectful if not discriminatory. As I said previously (and you agreed), having her appear in the wheelchair--or some wheelchair-like prop where she was comfortable--would have probably been better, anyway.
And I stand by what I said to you before. I would have been okay with Rhue appearing in a wheelchair or some similar device as a means of showing the effects of the eels on a person's nervous system. However, I don't believe her inclusion would have been absolutely necessary to tell the story of what happened to her. Montalban's delivery of the lines discussing her death was well done and conveyed what needed to be said, IMO.
I don't think Star Trek
actors are immune to recasting. Kirstie Alley was replaced by Robin Curtis in the next film to play a character who was much more important than Rhue's. Be that as it may, it's always preferable to use the same actor or actress when possible, as fans often become just as fond of the performer as they do the chatacter. If Bennett was thinking of replacing Rhue simply because she was confined to a wheelchair, I'm not sure if there's a punishment availible that would be enough for him. We don't have any evidence that he actually wanted to do that, however.
I don't think it was absolutey necessary to have Rhue appear, regardless of any health problems she was experiencing. I have hard time believing that she would have added anything to the story. Shatner and Montalban did a fine job carrying the film on their own, although strong performances by Nimoy and Judson Scott helped, too.