She can only swim 10 metres, but obviously not correctly or the teacher would not need to be right with her. This means your daughter needs to continue with her lessons for several more years to be truely competent.
My children swam from 6 months of age and completed the swim program at 7 years and went straight into squad training, where they concentrate on endurance as well as refining their technique in all strokes (freestyle, breaststroke, backstroke and butterfly). The children advanced through the levels based on ability, not age and they didn’t always move up the levels together.
My children can swim miles with proper technique, however if I was to remove them from squad lessons now they would lose this ability before they were ten (they are currently eight), so they know it’s important to continue on until they are at least 13 or 14, to ensure this skill remains lifelong.
They have periods of loving swimming and wanting to do extra sessions and periods of not wanting to go, but overall they really enjoy it and love challenging each other in sprints (who is faster) and distance (to see who gets furtherest fastest).
If your MIL does not like taking your daughter, change the lessons to a day when you can.