I don't see it either, it's not as simple as saying "oh all she did is put on an act for the scene". There was a month time skip, they had plenty of time to talk, she pretended to agree with Shinobu's idea the whole time only to off-script it at the last minute.
No further need to believe in good outcomes, just take it as we see it when 136 drops.
I still think it was a last desparete attempt to make Shinobu see her.She probably made made to be like "hey,i can do that too and i want you to only see mee".
She was showed as Shinobu who would do anything to Shinobu even if is a stupid thing like the scammer chapters.This type of stupid logic exists in many manga/manwhas stories and here i think we can apply that possibility too.
I think that logic of one mouth talk has also to be applied with Fuckboi and Sakura because they didn't solve their problem too.
In this story,one thing we doesn't have is proper communication,if we had this Shinobu and Sakura would never break up,in the story we had misunderstanding after misunderstanding and they had a bunch of time to do that.If we had communication Shinobu and Fumi could solve their problem and if we had a proper communication Sakura and Fuckboi also had to their problem.
In my opinion that one mouth to talk in REAL LIFE makes sense but in this manga communication was almost zero and in this case was nothing different from what we have seen before in the story.They only talked afterbsome big mess happen and that will be the case again here.