The mangaka knew what he was doing with that roof-top montage. Just play the Spider-Man theme over it.
Also, I bet she's trying to get his heart because she wants to have his "love" in her painting and put her heart into it.
I call bullshit on the blender thing, though. As an artist, blending organs wouldn't give you the kind of consistency you would want from a paint (even if you shook it up a lot) and it would result in a lot of physical texture. It also probably wouldn't be able to "stick" properly to the canvas and would drip down more like water. I'd say use blood, but blood is typically too thin and doesn't have a lot of pigment, unless you have a lot of it and use it with iron oxide.
This is to say, the more I thought about it, her plan kinda falls apart in terms of the ability to make an art piece that isn't just Sander Cohen levels of bullshit.