You are all being mean. Gopi is not stupid. She was in shock when she heard it was her sister behind all this - you heard her in the show saying she couldn't believe it at first, and was taken aback. She could not believe that Radha, her younger sister, her own blood who she barely even knows, mind you, because she never got the chance to really spend time with her, could ever betray Gopi and her family.
Eventually, after getting over the shock she realized her maa ji was right, and she was still in shock. Gopi was dramatic when she took off her headband and said she won't do aarti until both Radha and Tripti come with their nose rubbing the ground in apologies. But of course, apologies for the 8 years of suffering is not really enough. I believe Radha and Tripti should be hung for attempted murder, and Tripti definitely for Umang's murder.
As far as Gopi being stupid, she isn't. She is human after all, and we all tend to do some stupid things once in a while ourselves. We are not perfect. She has learnt to talk back and to at least support herself the 8 years she's been gone from the Modi house. For the most part, Gopi always has faith that things will be okay. So why not look at those parts of her instead of how she is so melodramatic and being stupid, and that Rashi is more clever than her, etc. Rashi may be more clever but look at all the things she's been doing in the past that shows her the opposite - clever and cunning but in bad ways. Rashi may have changed somewhat for right now to take care of situations with Kokila, and Gopi, but she still listens to her mom and she still does kalakaris all the time. Her mom is the one who tells her what to do for the most part. Rashi is not all that smart and she opens her mouth at inappropriate times too.
Anyways, these are just my two cents...to each their own about the characters. 😊