This one got me curious. There's an interview with Kathy Najimy where she gives some clues (but not a name) about someone who auditioned for the movie but didn't get cast and I just wondered if anyone might know who she's talking about:

Did they pair you with anyone interesting during these auditions? Anybody we would know now?
Well, yes, but I hesitate to say them because I wouldn’t like it if someone said, “Yeah, Kathy Najimy auditioned but didn’t get that.”

I get it. As movie lovers, we love the different calculations of what a movie might look like had someone else been cast. 
Here’s what I can tell you: a good singer, known but not as well known as her wildly, wildly, wildly famous sister who’s not with us anymore, but one of the greatest singers of all time. Can you make any kind of a guess?

Okay, let me think. 
And her sister was huge with the gay community, a huge legend.

Did they sing together?
They might have in their lives. The one who’s not with us anymore is older.

Maybe Donna Summer's sister Mary Gaines Bernard?   🤔   But maybe she is too unknown? Everything else fits though. Donna was very famous, huge in the gay community and is sadly no longer with us.

I didn't know Donna Summer had a sister. Like you said, the other stuff fits...I imagine being "known" to someone in the business like KN may be different sometimes than being known to the general population. She doesn't specifically mention if it was for the lead role which, no doubt, TPTB would have wanted recognizability and star power. Apparently, the lead was originally meant for Bette Midler, who turned it down.

48 minutes ago, applcin said:

I didn't know Donna Summer had a sister. Like you said, the other stuff fits...I imagine being "known" to someone in the business like KN may be different sometimes than being known to the general population. She doesn't specifically mention if it was for the lead role which, no doubt, TPTB would have wanted recognizability and star power. Apparently, the lead was originally meant for Bette Midler, who turned it down.

I didn't know that about Donna either, but I tried to think about who very very famous dead sibling could be, and she was the only one who fit. Apparently her sister sang with her.

Mary Gaines Bernard

Oh Donna Summer (R.I.P.) had quite a few siblings from what I have read. The recent documentary done by Summer’s daughters mentioned that Summer’s two sisters sang backup and often toured with her.

I think this may be Donna with her sisters. Gorgeous performances.