Board Thread:Speculation House/@comment-27404492-20170708180328/@comment-30530552-20170709171631

The way Weiss was saying it, she knew of its existence in V3E4. Lemme excerpt the conversation here.

"What do you mean? I'm getting better and better with my glyphs, I've even started time dilation!"

"And what of your summoning?"

"I...uh, *sigh* you know I can't..."

"Don't be ridiculous. Every Schnee has the ability to summon. We have for generations."

"I'VE TRIED. It's just--, its the one thing I'm having trouble with."

It doesn't give a 100% confirmation either way, but at the very least she knows of it, though maybe not necessarily seen it in action before.