Tana and -spd

Honestly, my Tana is the opposite of your -atk but +speed. She was also my first summon btw. Are you planning to use her as a defensive wall or an offensive frontliner? Thats an important issue bc if you will do the latter, use Swift Sparrow and an player phase oriented lance like Firesweep(+)

I do have a -spd +hp Tana, i run her with Fury and swordbreaker and she doesn't have much problems, other A slot can be her default one or close def if you have the fodder, for b slot you can also run lancebreaker or quick reposte

Her legendary weapon doesnt help her that much in my opinion, so using any of the refinable Lances and refine it for speed may do the trick, and you may get a interistin build out of it.
As A Slaying spear against armors, or a ridersbane agains cavalery