The gemara cites a braisa where the chachamim went to visit Hilni HaMalka and found her sitting in a Succah higher than 20 amos and didn't say anything to her. Rav Yehuda uses this as a proof that a Succah higher than 20 amos is still kasher. Although a woman is patur from Succah so there is no proof from their allowing her to remain in such a succah, the gemara says that since she had 7 sons which must include children above the age of chinuch, she would have followed the chachamim who told her to ensure that the Succah was kasher for them. Rav Yehuda therefore concludes that their silence indicates that they considered it to be a kasher succah.
There is a discussion in Tosafos Eiruvin 96a whether a woman who does a מצות עשה שהזמן גרמא is in violation of ba'al tosif. The Maharatz Chiyus points out that our gemara should prove that it is not a violation of ba'al tosif, otherwise Hilni HaMalka should not have been allowed to sit in a Succah. The Maharatz Chiyus explains that perhaps the opinion of the Rabbonon was that since the Succah was indeed passul above 20 amos, they allowed her to remain in it without a concern of ba'al tosif.
There is a major machlokes between the Rambam and Tosafos (Kiddushin, Rosh Hashana) which develops into a machlokes between the Mechaber and Rama (hilchos tzitzis) whether women can make a bracha on מצות עשה שהזמן גרמא. Although we don't consider it ba'al tosif, and consider it to be a kiyum mitzvah, the mechaber holds that it is not a sufficient level of mitzvah to warrant a bracha, whereas Tosafos and Rama hold that it is a mitzvah that warrants a bracha. According to Tosafos and the Rama it should follow that Hilni HaMalka was likely making a Bracha on the Succah, therefore even if the Rabbonon held that she and her children didn't need a kasher succah, they should have said something to her to prevent her from making a bracha l'vatala? The fact that the Rabbonon justify not mentioning that the Succah was passul because she was exempt from the mitzvah implies that she wasn't making a bracha, which supports the opinion of the Mechaber and Rambam.
I once visited a single older woman on Succos and realized that her succah that she was very proud of was completely passul. I was considering whether or not to tell her. This gemara seems to support the idea that it is unnecessary to say anything. Fortunately she was a sefardi woman who didn't make brachos on mitzvos. Had she been making a bracha on the Succah, I am not sure if there would be justification to remain silent.