Baby switched to nursing on one side only

Has anyone else had experience with this? My daughter has recently started deciding she’s full after nursing on one side and is refusing the other. She’s gone from nursing on both sides for about 30 minutes total every 3-4 hours to nursing on one side for 20 minutes every 2-3 hours. She is getting enough milk, the number of wet diapers each day hasn’t changed.

Should I pump on the side she doesn’t nurse on or am I fine to wait until the next feed? She doesn’t take bottles right now so that milk won’t be used to feed her but I don’t want this to have an effect on my supply.

She’s 4 months old.