As a Harley main, picking up Shayera, I think the MU COULD be 5-5, but it feels to me like it leans close to 4-6, Harley's favor. Yes Hawkgirl has her hideaway spot to avoid MB cupcakes and the air shots, but her flight does come to an end and at that point she will feel Harley's flurry of projectiles. This is a MU similar to Wonder Woman, in the sense that both on the ground(Harley vs Hawkgirl), is anyone's game though imo it's slightly in Harley's favor due to superior mix ups and frame traps, but Harley at a distance can chip HG out while also evading her maces giving her already the life lead she needs to wait for the timer to run out. Not to mention any hit confirm combo starter Harley gets will dish out on average a 40% meterless combo which she can in the end use up 1 bar of meter to MB her Play Doctor which will cause an additional 8% unblockable damage while leaving her safe to play keep away again.
Long story short, its a MU where Harley can play keep away better and even if Hawkgirl wants to take the fight to her, Harley still has the upper hand, though not by a significant amount, but still on top. I spent the last 3 hours facing the AI Hawkgirl as Harley on very hard(yes its the AI, not a human, blah blah, however) and in the end Harley was winning nearly all of the matches. There was no routine so that I could "outsmart" the AI to get a cheap win, and to add, the AI would IAmace charge on reaction whenever I jumped on top of optimizing many combos whenever she would land any; higher combos and faster reactions than humans I faced, so to me that was saying something. As well as with me, I would evade maces on reaction, not through routine, which isn't really hard at all though, but just saying.
The way I see it, if HG wants to win this MU, she has to do whatever it takes to get the life lead and wait for the timer to run out. Flight will not help her accomplish this in this MU, believe me, and being up close and personal is a risk in itself. Not to mention Harley gains a HUGE amount of meter in this MU, this MU is like a surplus of meter for her, where Hawkgirl will most likely not wager because she WILL lose. Thoughts?