1) She must have been there yesterday. (I´ve come to this conclusion)
2) She must be there now
3) She must be there tomorrow (next week)
Is sentence #3 right? Can I ever infer about the future?
What if I´m not completely sure if she will be there tomorrow?
She could be there tomorrow.
She might be there tomorrow.
She may be there tomorrow.
She can be there tomorrow.
Which sentence implies the strongest probability? The one with "could"?
As for should, as svartnik mentioned, where would it be on this list of probability? Higher than may?
This sounds rather artificial to me. The last three all mean the same thing. If you want to express a probability, you'd use adverbs, not a different modal.
Would you actually make these distinctions in real life, engee?
* "She could be there ... actually, no, I'll go so far as to say she may be there tomorrow".
Much, much more likely:
"She could be there ... actually, no, I'll go so far as to say she probably will be there tomorrow".