Shifting problems

Drove my granddaughters car for a few miles in just D and it was shifting fine through all gears and back. Then put it into manual when I was stopped and drove off and manual shifted into second gear which it did, but then it suddenly shifted back to first which made the engine tach up. So I put it back into D and it read D1 on the instrument panel and would not shift from there. I then stopped the car put it into reverse then back into D and it showed just D. I drove off and it shifted to second gear then went back to D1. All this time there was no check engine light shown. Hope you can help.