My DD also prefers one side (rightie), which has always been the powerhouse with a forceful letdown. Leftie is the shy, retiring type she still takes it, but gets fussy quickly.

My SIL BF her second bub off one side only for months, after the other 'dried up'. He was and is a happy, well-fed little rascal.

Have heard it's very common.

Good luck, hope it goes well and I also highly recommend contacting the ABA if needed. I've called the hotline loads and the ladies are so helpful.