Cause-effect

No, it is not. Indeed, the fact that event A (rain) always causes B (cat's sneeze) does not mean that B causes event A. This is one example of a very common sort of logical error, the confusion of a statement with its converse.

The cat could sneeze every 5 seconds!

the cat is ill ,i think

What if the cat also always sneezes just before it snows?

According to this question, Cat always sneezes before it rains but that doesn't mean for every sneezes.Here rain is taken as the reference.So the answer is no.

This is a "post hoc ergo propter hoc" fallacy, a Latin term which translates to "after this, therefore because of this". It states that "X event happens, Y event follows. Therefore, Y event is caused by X event". The event is concluded solely on the order of events, disregarding all other factors that might rule out the connection. One example is "I'm not going to invite John to the picnic anymore since it always rains when he joins."

The statement says that "alice's cat always sneezes before it rains " it does not says "alice's cat only sneezes before it rains" it is guaranteed that before it rains the cat will always sneeze but it is not guaranteed that cat cannot sneeze sometimes else more precisely "it is not guaranteed that it always rain whenever the cat sneezes "