They don't have to give you 'every choice'. There should be simply a way to say that you don't want to do it and have the quest marked as completed.
You don't have to complete every quest you get - What if you change your mind later?
Unlike
Morrowind, if someone asks for your help and you're busy or unwilling to perform the task at that moment, you're allowed to say "No" but change your mind later. You can always ignore "incomplete" quests.
This quest will only "finish" if Grelod dies, because that's the condition. There's no way to "fail" the quest, unless Grelod somehow finds a way to become even more Immortal than any Daedra: Even if she were to become a god, she can still eventually be killed.
She's so stubborn and intimidating that
all demands that she step down from the orphanage have the same answer: "Over my dead body"