N.B.
Training pants are mostly for the convenience of the parent. As you say, they make accidents easier to clean up. At 3.5, she should have a grasp of what is expected, but there is no down-side for her. My suggestion would be to take her to the store for some cute big girl panties, let her pick out the ones she wants(they have Disney characters,etc.), and make a big fuss about being a "big girl". Throw all the trainers out, and each and every accident is handled by her, with you coaching her about what needs to be done, but not doing it for her. "Oh, I see you're wet. You need to take the wet ones off. Now put clean ones on. Now put the wet ones in the laundry(or stand at the bathroom sink and wash the poopy ones). Now clean up any puddles on the floor. Then you can go back to playing." No criticizing, no punishment, just taking care of business. This is no different than having her pick up her toys. "You made the mess, you need to clean it up. " She won't wash too many panties before she realizes it's more trouble than it's worth. Good luck.