You are correct. But if by discussing it we brainstorm an idea that would help pinpoint where Lisa was likely put into the river, then we could direct a search in that area.
Say we discovered that someone was seen throwing something off a bridge 2 miles downstream. If there are cameras on the bridge, it's possible that LE could review those and determine if it's possible Lisa that was thrown in, then begin searching.
We all want Lisa found, preferably alive, but if her body could be recovered I think that would make a lot of us feel better. So trying to determine where she is, is beneficial in my opinion.