Peach is so fun to play and I really want to main her, but at the same time, I'm terrified to play her because I don't want to create any bad habits. I need to ask the Peach boards about how to begin playing her, but I haven't gotten around to it yet.
Dtilt has a deceptively large hitbox. You can stand decently far away and still hit. I'd say just play around with dtilt in training and see if you can get the spacing on it down because Peach is all about being safe. Also, I'd recommend looking up the QFR (I think it stands for Quick Float Release, but I'm not sure) and learning that. It really improves Peach's poor mobility. DarkPch made a guide for it, but I'm not sure if I can find it again...I'll look and see.
found it:
here you go
it's kinda difficult but it'll make your peach a lot better.