Mary is a supporter of free will. Thanks to a time machine, she travels five minutes into the future and finds out that she will quietly drink a coffee. She goes back and decides not to drink it, to reject her discovery.
It follows that:
1) Once back in the present, something will force Mary in a few minutes to quietly drink a coffee. Even if this hypothesis is logically possible, it sounds not very persuasive.
2) Time travels are impossible.
3) In returning to the present, Mary find herself in a different time line. Consequently: a) there are several universes, b) in some cases it is impossible to visit the future of one's own.
4) Mary doesn't drink the coffee and changes the future. In this case, she had previously not visited her future, since she saw herself drinking a coffe, and this is not the case anymore.
is there a better answer, or it's just opinion-based?
This thought-experiment is inspired by a time-travel loop from Time and Space, by Barry Dainton:
The Marriage Decision Mary is torn between two suitors. She can’t decide whether to marry Tom or Jack. So she travels to the future and finds out that she is happily married to Tom. She then travels back, and marries Tom for this reason.