means this in English
Personally, I would not say that those two phrases mean the same thing.
So many times, I've heard people say 'you have right' or even 'you have a right' when they mean 'you are right.
So have I, being in regular contact with Poles who are learning English. But if that was what was meant in the reply, then you would think that she would have said, " I think that she has right " instead of " I think that is her right ", although in the context of the sentence, that reply doesn't make any sense to me. What would she be right about?
I think it's more likely that she meant she has a right to do this, as in seeing someone else, but who knows? We're all just guessing here!