Judging by her twitter, that project is still going on.
A gentleman will not insult me, and no man not a gentleman can insult me.

I originally was going to watch it just to see Kaia Gerber's acting debut and when I saw that Michelle Trachtenberg was also in it, it made the film so much better. Everyone did a great job.

I'm halfway through it. Its good.
In the kingdom of the blind, you're the village idiot.

It's released on 17th September 2016 in the USA, according to IMDb.

I just hopped over to Sister Cities IMDB page, it is now listed as completed. No release date though is mentioned.

'Sister Cities' sounds like a really interesting movie

Saw her mentioning she was cast in a new movie but there was no details at that time
Anyway found this review of the play which mentions the characters
Mary is the mother
Michelle is Dallas according to IMDB
Carolina is forty, a hard-driving lawyer, and is recently divorced.
Austin is thirty-six, lives with Mary, is a successful writer, is athletic, and, much to Marys chagrin, is gay.
Dallas is thirty, the archetypical sorority girl, is a school teacher, and lives in the suburbs with her husband of several years.
Finally, Baltimore is twenty-six, the youngest of the bunch, whos trying to find herself as a graduate student studying sociology at Harvard.
..Later, we learn all four sisters have skeletons in their closets that theyve carefully concealed from one another.
http://agoodreedreview.com/tag/sister-cities-review/
Carolina, the uptight lawyer,
Dallas, a prissy schoolteacher
, and Baltimore, the wild child
http://www.stagebuzz.com/2007/11/review-sister-cities-t-schreiber-studio.html
Film biz where thieves,pimps run free,good men die like dogs.There is also a negative side.

Nice
You shall have no other Kates before Kate Winslet.