After the Queen's first plan -- asking a random dude to murder an innocent girl -- somehow fails, she decides to take the matter into her own hands. She creates a poison apple that will put Snow White into a comatose state until she's awakened by "Love's First Kiss." The Queen reasons that the dwarves, thinking Snow White is dead, will bury her alive, thereby ensuring that no one will ever kiss her. Personally, we wouldn't rule out committed necrophiliacs, but we guess that's why we don't write for Disney.
"Sleepsual assault is as far as we go."
So why did the Queen choose literally the worst way to take out Snow White, short of feeding her regular apples until she got too fat to compete in the high-stakes beauty pageants that apparently rule this realm? We get that the Queen is using magical poison in the film, and that maybe these side effects and qualifiers are listed on the fine print of that particular concoction. Hey, you know what's a lot like magical poison, but without all those loopholes? Regular goddamn poison.
Or a crossbow. Seriously, just a bolt to the wordhole, while singing "I'm the Queen, that makes this legal!" Boom, done.