It took me awhile to learn a lot about Harley. She has some of the funkiest inputs in the game. Play Doctor can be done naked 100/100 times but when you try throwing it in combos it always seems to not work or send out gun shots instead. Same can be said for her tantrum stance, it is so strict on it's input that if done incorrectly you'll just back roll instead of being able to 1,2 or 3.
Best advice I have for Play Doctor is go to practice mode and keep practicing these corner combos until you can get your timing down. Once you get it a few times you'll start to see how easy it really is.
J2, B22, Tantrum, 1, F13, F13, 12, PD
J2, F2, Tantrum, 1, F13, F13, 12, PD
J2, 2, U3, J2, F13, 12, PD
12, Tantrum, 1, F13, F13, 12, PD
These are her easiest corner combos to practice her timing with (for me anyway). You'll want to mix them up so you don't put too much muscle memory into just one combo. Once you can land all of those 9/10 times move on to the mid screen combos with PD. Such as:
J2, B22, Tantrum, 1, B3, J2, J2, 12, PD
Just stick with it, Harley is a beast.