blackcat, I am wondering if you could ask her to practice the cello during the same timeslot as when she is practicing the piano - if she is out of focus at the end of the day, she could either practice cello and piano back to back or reduce piano time on alternate days and practice cello at that time when she has more motivation and focus.
I am all for discontinuing instrument lessons when the child refuses to practice, but, I have known many adults who had regrets that their parents did not push them enough to continue on an instrument. I don't know any adults who were upset at having learned an instrument or participated in orchestra. So, it may be worth a little extra effort to reschedule her day so that she has more time to work on piano + cello in a continuous session.
I also like the idea upthread about providing her more interesting sheetmusic if she does not think that the orchestra repertoire at her level is challenging.
