>>109140606I think although it might seem counterintuitive that she maybe can't.
Having an actor from an old show or movie appear as a new character is a nod to that actor's history and roles. Having them appear as a specific character - either the original in a given production, or a character which infringes on the rights *in that particular production* is a different thing.
For example, Harvey Keitel can sell insurance as "The Wolf" because someone at the insurance company's ad agency is good at contracts and licensed that from whoever owns Pulp Fiction now that Miramax is dead.
Having Helen Slater appear as "X Danvers" in another iteration of Supergirl is fine because Danvers is a name in the property and she's not playing Supergirl.
Having Helen Slater appear as "Supergirl" from or representative of the Salkind-produced Supergirl movie might not be possible *if* the Salkinds' rights to those movies they produced are still current and if they are unwilling to license the re-use of their own production, which, to be fair, they do own. WB holds the distribution rights to those movies of course which is some leverage, but it's a question of whether it's worth WB actually bothering to deal with the estate of two notoriously difficult producers.
This was for many years the problem with releasing the Batman tv show on home media - it was co-owned by three disparate companies - and is more widespread than you might think. Even today we have characters from the FOX-produced Gotham tv show who should, by rights, appear in this crossover, but won't because it's never been licensed to be produced that way.
Other characters - like Brandon Routh as the Salkind-derived Superman/Clark Kent - are fine because in their particular cases a movie has already been made (in fact two movies, Superman IV and Superman Returns) under the rights originally owned by the Salkinds, so any legal legwork that needed doing is already done. But Gotham remains a glaring omission.
