Lots of tempting choices for leveling. Depends what your focus is. Judging by your roster, I would guess CB. If so, your CB team could be something like:

FB (poison + poison sensitivity)

Ninja (raw damage)

Fayne (poison, weaken, DEF down)

The remaining critical pieces to fill in are ATK down and DEF up. Other nice things to add would be Counter/Ally Attack and block debuffs/cleanse debuffs/

Other interesting choices to level:

Cardinal makes for a great arena choice, since you can focus on gearing her tanky and then the rest of your team can be glass cannons.

Mordecai will eventually be useful for you in Spider, most likely.

Spider is a nice budget arena debuffer and nuker.

Khatun is always a great choice. Same for Apoth and Armiger.

apothecary and spider. Dragon 20 should be your goal

The overall stats of your FB are quite low. You need better gear. Trips is right, Dragon 20 should be your next goal to improve your gear.

What gear do you use on her? Even if all stats are quite low, the attack and critdamage (without critrate) seem higher than necessary. FB doesn't need hitdamage, she just places poisons. Even healing through lifesteal gear works without the raw hitdamage, you can heal from Warmaster, wich counts as damage for healing pupose with set or leech debuff.

You got the right idea, accuracy is the most important stat and the value is ok (as a rule of thumb: dungeonlevel x 10, so 191 will do for a while). But her defensive stats (HP and def) and her speed are to low. The wave guards in higher dungen stages hit hard, all champs need some HP/def to survive that. And in general you want more speed to get more turns for your champs.

Speed  boots  are  definitely  a  requirement  unless  you  have  Defense%  Boots  with  Triple  Roll  Speed  or  higher  on  6  star  gear.