Well, perhaps, but if she found out I would have thought she would at least try to stop the torture, which goes against the idea of the scene.
not directly, rin is aware that while torture is bad failing to prove the matous guilt is worse. i mean if she were to break into and steal sakura away she only succeeds in screwing her and sakura.
Well, it's not so much proving their guilt as proving Sakura's innocence (or, at least, enough doubt about her guilt to stop Nero sanctioning the torture) but, yeah, I guess. Breaking in might save Sakura a lot of pain, but it will also make it a lot harder to get her free in the long term.
Having said that, though, if she has any real influence with Nero she could at least persuade her to stay the sentence until she had a chance to investigate further, which would obviously stop the scene going as planned.
I think the basic concept does work, though, and it would explain a lot of what Rin was up to. I think we should attempt to tie it in with her meeting Archer, though. Perhaps she seeks out his help or something (maybe she is initially planning a rescue, either to stop the torture or if she can't prove Sakura's innocence).
Also, how would he end up paired with Rin in such a situation?
becoming a famous and strong gladiator would make her take notice of him, i assume she would pay his debt after that
Ah, I see, so basically she buys him out of his debt because she likes him?
I would imagine it would need more than just "taking notice" of him for that, though....