When you D-throw Peach, if she DI behind you, I do U-tilt/Uair and keep her above me with more Uair.
If she DI away you can regrab to just under 30 I think. After that what you do is mostly whatever but I like simple Fair.
If she tries camping back with turnips, just charge a full set of needles and time them to hit her when she's plucked or thrown it.
To approach now I run at them and WD down about the distance of an F-tilt and a bit more at them and then wait for them to do something. Or I SH so when I land I'll be just over a Bair's distance away from them and then if they approach I Bair them through it and if they don't approach I land and then wait because I'm still at that distance. Or, alternatively, I double jump and waveland or something or jump away with needle charge or throw needles.
It is extremely advantageous to be behind Peach when she is in shield.
I'm finding the biggest problem with people vs Peach is that they try to be super fancy with needles and stuff when she's floating at them or they do the wrong things at the wrong time. They'll FJ onto a platform and needle and then platform drop and double jump into more needles when they Peach is approaching high in front of them with Fair rather then jumping above Peach and descending with Nair, or - for the more practical - SH Bairing at them. Or, for the even safer, just waiting for Peach to land and then running away or kicking at that point.
Don't be fancy... kick her when you're supposed to kick her, needle her if she's trying to camp you back or if it's convenient, and don't get stuck with no room to jump back and Fair. If you do get stuck, Up+B stall, do a perfect ledgedash and get your breathing room back.