My daughter is 3 next month, she is fine with going potty at home as long as she isn’t wearing any bottoms. As soon as we put her in knickers and trousers, she won’t go potty. We explained the knickers, that it isn’t a nappy and she always seems to understand, but still doesn’t go potty.
At first I thought she just forgets, but this has been happening since May. We tried rewards, a reward chart, doesn’t make a difference.
We make sure to regularly remind her just in case she needs to go, but unless we put her on potty ourselves, she won’t go. For example just recently I asked her if she needs to go, she said no. 15 minutes later, she did a number 2 in her knickers 
Any advice?