Both Kramer and Streisand are histrionic people with huge egos. It's hardly a surprise that they had trouble working together. Streisand might have done an honorable job by the play, but we'll never know. And, frankly, I'm going to take what both of them have to say here with a grain of salt.
As for Streisand playing Emma in the current film version that's in development, I don't think it's a great idea. She's 25-30 years older than Dr. Linda Laubenstein, the basis for the character, ever lived to be. Emma is described as being in her late thirties. Barkin can play younger, Streisand really can't.
"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