The constraint is always raw material. She has no shortage of ideas or time in which to put them into practice. Hence, she is most avaricious in acquiring hearts whenever an opportunity presents itself. Having a stockpile means she need waste as little time as possible.
"Well, there's fun we can have with physical means - I am quite the fan of knives - and fun with magical - which requires a bit of finesse, but, well, there's always more prey about. Depends on which path you'd like to take."
Then the Yew Queen can show her all the many, bloody ways of physically terrorizing someone!
And then teach her healing, so they can start all over again.
"Kill her or set her free, possibly after healing her. Some people like taking trophies from their prey, too, but that's your choice."
Shade looks over the girl consideringly. "I don't think I need a trophy. Nor, I think, do I wish to let her go free."
Shade puts her foot on the girl's throat and presses down slowly, until she feels it collapse entirely.
"I'd suggest more practice. Either in magic on its own, or in the practicalities of hunting. Or we can plan our hunt tomorrow."