Praying the rumors are true. The film started principal photography on August 18th, meaning that shooting should end around late October. Sarah Chalke was just announced last Monday
http://bit.ly/1FNvEZD, so there's still hope.
My only thing is why would she agree to shoot something else while Younger is shooting unless she doesn't have many scenes on the show (like last year) again. Atlanta is only 2 and a half hours away from NYC, so I could see her taking off for two to three days to shoot a small role without having to worry about jet lag. But it is curious as to how this role may have come about, if the rumor is true.
The last two films weren't critically adored, but as others stated, the exposure would be really good for her. We all know H does the least amount possible for her career, so it would be a throwback to the good old days.