Sorry to hear about the young woman's passing.
At the time the Swank production was happening, her career had cooled significantly. It had been several years since she won the Oscar for
Boys Don't Cry, and her only other major film role during that time,
The Affair of the Necklace, was a flop. (She had a supporting role in Christopher Nolan's
Insomnia, which also underperformed)
Million Dollar Baby hadn't happened yet, and she was definitely looking for a play to give her career a jolt. I believe she was committed to Arthur Miller's
After the Fall for Roundabout at one point, but that didn't end up happening with her.
This
Miracle Worker did an out-of-town tryout in North Carolina that seems to have been a fiasco. The reports are that Swank wasn't confident in the role, and the production (directed by Arthur Penn) was all over the place. The Weisslers, who were producing, decided that it was in no shape to come to New York and pulled the plug. I find it hard to believe that it would all come down to the availability of one of the play's male actors, considering that neither of the major male roles are really make-or-break, and neither of the actors cast in those roles were name actors.
There was also the matter of Swank only doing a seven-performance week, with a Wednesday matinee alternate.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body