>>103865602
I don't think recording separately makes sense, it's way too seamless for it to be a transition between live capture and playing back a recorded animation.
What I think is most likely is they had someone nip in to give her the violin and bowstring and then quickly take it away after.

It's hard to tell because of the camera choices, but about 10 seconds before the violin model appears when the camera is focussed on Mococo, Ceci's right hand noticeably appears to grasp something. In the vod I have (linked above in this thread) this is at about 54:49. She's also holding her hands in front of her in the subsequent shot before turning around, whereas Ina has her hands to the side.

Then, right as the violin part ends, she releases her hands and someone catches the stuff. This is possible because everyone else is out of the way and Ceci moves to the left, away from where the person would be standing to her right.

She'd have to be pretty damn good at getting it into position quickly though, she does it in a single smooth motion. Must have practiced that a lot.