That's something even I read in the interviews, that Claudia was cast (or I would say officially signed on) only after Eric Stoltz left. But the photo is a clear evidence showing that's not what happened. Looks like they had early test shoots with Claudia, even though Melora Hardin was in the running for the role. Melora of course appears not to have any photo shoots done during her short while when she was part of the production.Yes, it's really Melora Hardin on that photo. Claudia Wells was cast only after Eric Stoltz was replaced by Michael J. Fox. Hardin was too tall for Fox, so they had needed another, smaller actress.
That is definitely not Melora Hardin, just looking at the face especially the eyes, hair it's pretty evident it is Claudia Wells.
I know many keep seeing it as Melora Hardin, but I won't go any further to convince anyone otherwise