Dude, she tells Satoshi that if he says he still loves her after the show, she will come back to him, it's the same thing she tells him to accept what she become by having sex with Kendo, a big cock loving slut because if she had no intention of going back to him that would just be cruel
She did have no intention of going back to him though. She says as much. You can see it, because he does still want her after that and she does not go back to him.
She says directly that the purpose of that "show" is to get Satoshi to hate her, so that he can have a clean break. And yes, it is incredibly cruel. And it's isn't very smart. Because Mary didn't know how determined Satoshi became to win her back after the arato incident, she thought that this would be a final break for them.
She didn't have any intention to get back to him when she proposed those dates even. They weren't really tests, Satoshi never had any chance of winning them. Marys intention with those dates was to tell Satoshi about his flaws that she perceived during their relationship so he wouldn't repeat them when he dates someone else.
It wasn't a good way to do that, but that was still the intention of mary. After the Arato incident, there was not way for satoshi to get mary back. They were basically already broken up and what mary did was meant to prepare Satoshi for the future, even if it did so in a very bad way.
Kendo didn't make her do the show, Kendo didn't even know that was what was happening until it already started. And Kendo's sex certainly isn't the reason why she still doesn't get back with Satoshi after. They had sex marathons like this plenty of times before.
If you seriously think that Mary had any intention of getting back with Satoshi at all when she organised that "show" then you just didn't pay attention.