Most of Wonder Woman's losing match ups were to characters who could zone her out. It's been a while but I believe they were Zod, Sinestro, MMH (on certain stages), Lex and maybe Aquaman. She struggled with the latter two because of their traits negating her ability to start her offense in addition to the range on their normals and zoning ability. Jumping was not an option at all against the first 3, who also had very annoying traits to deal with. Her lack of full screen presence and difficulty getting past their zoning allowed their traits to (re)charge pretty easily as well.
She did fine against the rest of the cast and even beat some zoning characters like Deathstroke and Zatanna. It just required a lot of patience and it could be very frustrating at times. She was a very solid character, possibly even top 10. I wouldn't mind her having more range options and the ability to reflect projectiles. I hope she doesn't lose her great lasso normals and combo starters.