Riot senna support sucks

She's got a 49% winrate? Senna support is fine.

{quoted}

Please fix it as I am tired of having to lane with her as my support.

(Speaking as a Senna main across two accounts, each with her to M7)

Then you're making absolutely no effort to lane with her correctly. Senna likes to trade in shorter bursts, or go all-in if she lands her root on a champion. If you do nothing to help her when she's trading/going in, no wonder you hate laning with her; she can't heal you because you won't be in the area of her Q, she can't count on you to help deal damage because you've gone back to base already, and she generally can't do anything because you haven't done anything to help her when she's just trying to get you fed.

Senna is, at her core, an aggressive support, and wants to get you fed by going in. She has a decent amount of bail-out for if you/her get caught (ghost form, heal, root), but her spells are definitely intended more to be used aggressively than defensively. When she hits a root and it isn't to bail someone out of a bad spot, that's generally your sign to attack that target. 9 times out of 10, you WILL get a Flash from the enemy just by aggressively positioning to follow on a root, or snag a kill if you already got their Flash. Even if YOU PERSONALLY don't get it and Senna does, that's still a 400g swing in your favor, a lot of breathing room to farm (a 2v1 bot lane generally guarantees the surviving enemy can't do anything to you), and usually a tower plate or two (another 120g split between you two per plate).

If you make no effort to play to what Senna's strengths are, consider that it might not be her fault. It might be you not doing anything to help the support that's been trying to help you all game.