I got her free as well myself, but honestly she might be worth it.
Why? Out of all the characters, her talent tree is the only one that actually feels unique. There isn't any (or at least for the most part) "+X % Only" talents. All of them have some little trade off, or introduce some slick little trick into her bag. Ordered Chaos in particular really seems to have its own unique playstyle, while Little Big Trouble has plenty of fun little tricks and the Friends tree has a few quality of life talents in the beginning, as well as some nice ones later on.
I'd say maybe look at her talent calculator, see what skills you like, mess around in it for a bit, and if you are digging it then maybe grab her.
Also, Gaige/Mechromancer does NOT come with the season pass. The Season Pass is exclusively for the expansion-like DLC releases, like General Knox or the Clap Trap Revolution DLC from the first game. NOT classes. --- "they'll be too busy yelling at the whiny 12yr olds playing on their Xglove 36k Omnitools playing Call of Duty: Shanxi at War" ~cursedseishi~