I don't think she needs a buff. Indicated by her top 3 jg position for the past year and a half it would appear the exact opposite. She is really oppressive atm once Evelynn players get good enough to remove what was meant to be her counterplay. Namely her W prep time and arrow indicator. Done properly she will Q to hit them the instant the charm is fully primed, revealing her self before the arrow does. If she were to recieve extra AD scaling even on just her E it would require retweeking the more problematic elements of the WQ combo.
There's also the issue where late game comes along and she doesn't even need to fully prime W and can just EQR instagib squishies, only needing to charm for the MR shred on tankier carries she shouldn't be targeting in the first place.
Some combination of an earlier arrow indicator during the charm prep, shorter Q1 range, and less MR shred would open up a lot of power budget since she would have more meaningful counterplay. For E specifically getting an AD ratio, it would also need lower base damage by rank (The flat damage portion). If it was purely a portion of her total AD or a stronger scaling from bonus AD, it would result in the same situation as before where a pure AD build would overshadow the use of hybrid or on-hit AP items like
. With a combination of flat damage and total AD scaling, it scales worse with high AD stacking but better with the first few extra AD.
So, with the extra budget personally I'd go for 5 extra base movement speed for her pathing (bringing it to the same as before her rework and up to fellow jg assassin
's, a 50% total AD ratio on her weak E's flat damage (55/70/85/100/115 -> 25/40/55/60/75 +50% tAD) and a 75% total AD ratio on her empowered E's flat damage (75/100/125/150/175 ->30/45/60/75/90 +75% tAD), and apply two on-hits from her empowered E to targets hit.