The beauty about Ursula is that she held up her part of the bargain, gave Ariel 3 days to kiss the Prince. Nowhere did Ursula say she could not interfere. It reflects how real life contracts work... Student loans for example.
That's not how logic works. You just said: X is not in A. X is in B. Therefore, if X were in A, A would not go to B. This is not a valid syllogistic form. For example, here is an argument of the same structure: Guns are not allowed in school. Guns ar