The vibrato on the cello does need to be in time with the music. Teacher didn't know. Or didn't remember she said. I couldn't tell by listening but I'm good enough at vibrato now that I can feel it. Started Bloch's Prayer which at least is a decent song, finally.

Lack of enough good songs caused me to lsoe interest in piano. I've continued on with cello despite same issue because I've invested quite a bit of my money now. Not so easy to quit.