hi M., it sounds like your daughter is doing great, and like you are doing a great job with her too. and if she is interested when you go to the bathroom, i would just put a potty in there and see what happens, especially when she goes in with you, i bet she will just start to copy you and do it on her own.
i just wanted to say something about milestones ...it is very easy to get all caught up in when our kids "should" be doing things, some people get absolutely nuts with the milestones, though more so when their kids are on the other end of it, and not ahead like yours. just remember that all kids are different, the milestones are very broad, or they should be, anyway. i would ignore any charts that give too narrow of a margin. there is a very wide range or "normal", it really breaks my heart when i see people getting all crazy about their kids not being where they "should" be (to a point, of course, you cant ever ignore things that need attention), or even worse, making the kids crazy by pushing too hard. when she goes to school, you want her to still be interested and have things to learn, kids that are bored in school often have just as many problems as kids who are struggling to keep up, and they are even often misdiagnosed with various things. it sounds like your daughter is doing just fine, keep doing what you're doing and keep it fun, it sounds like you are doing a great job. take care, D.