It shouldn't stack, but it pretty much goes off every time she got hit? I just got her fresh so I have no idea. I'm quite confident it has the same mechanic with Wutan detective-chan though. But with 65% atk down (it capped at 70%, so I guess it's one out so I can bring another in) Stock should be fine for quite a time. Oh, what about your pillow girl? Is she good with many weak point target skill?
Edit: Please help me choose 2 out of 4. Give me reason why I should go with too will be very much appreciated. (You can use waifu reason like 'she hawt!' too of course.)
1. Oncidium bride ver.
2. Higanbana miko ver.
3. Snowdrop
4. Lavender valentine ver.