What's the biggest struggle right now?

Hi, new girl here. I have an almost 2 1/2 year old who just does not care. She "can" go on the potty and does it right away if she wants to but she just does not care. Her diaper can be drooping to her knees with pee or poop and she just does not care, she has never cared if she's wet or messy, she's too busy to deal with it. We also have a 7 month old (who does care if she's messy) so diapers are getting expensive. I knew it would be harder once she became a big sister but I'm ready to start saving some money on diapers...but not ready to enter public restrooms all over town.

I'm trying not to push her too much, we've tried panties and she has done well but only if she agrees to put them on, she won't always agree. She did pick out her own "Jingle Bell" panties (aka Disney Princesses).