Sorry i've never had a problem with Elise sense she dropped, i was honestly surprised when i saw she got a buff in the Zed patch, because i've only lost a few games as her. Though even then i'd tend to break almost even, or still be positive. As far as i'm concerned AP is lack luster on her, magic pen and survivability being more important, and if you stick to the outside of a team fights, fling spells, and jump on runners or an exposed AD carry she works great. Her spiderlings are great for eating skill shots, and her spider e is amazing escape (if used correctly).

Ap isn't as important, but if you are safe enough, with your current gear, a deathcap does not go unnoticed.

see i tend to think her early game is really weak and her late game assassin skills are amazing...kinda like tristana, easy to destroy in lane mid levels, but if the game goes on too long, expect to see that grey screen a lot

I've played her AP mid and AD top a lot, in both situations I find she does very well against the usual opponents (especially any with skill shots) while doing worse (but not terrible) versus those with targeted abilities. Since the buff to her AP ratios she now works well from early to late game rather than falling off later as AP. If you have any issues with her damage, make sure you're building Q first,then W. also for that extra survability as AP, make sure you have flat mr yellow and blues + the mr points in defense via either a 21/9/0 or 9/21/0 spec (she is a bruiser, so the defense is needed).
Anyways, main thing. learn to form shift a lot to make sure you can clear waves and conserve mana. Also it helps a lot for your burst, Q > spider Q > E allows for some great burst while making sure you're not put in any danger

POST EDIT

Forgot to add that I think her human basic attack and Q have to short a range by about 25-50 units.. she'd have a much better quality of life with that little bit extra

I've been jungling with Elise and she is REALLY good there just when it comes to team fights you have to go at it differently then ganks. Build some CDR and when it comes to the team fight stay in Human form for a bit to harass with W then once you see the proper opening hit someone with E, transform, E them again and go to town.

She is sitting at 50% win rate after patch. I think she is in a good spot.

She's not as up as Syndra. Annie has a worse late game than her.