How come? I played like 10 times with duelist and won 3 or 4. Her problem are ranged enemies you have to get something to handle them then melee she wrecks everything. I admit if I get to big robo without something good for ranged enemies I reset.
My usual advice is to look at how you are dying: not enough food, getting killed by a particular type of enemy, boss too tough, etc. The game gives you ways of dealing with all of these. You can experiment and see if you can improve your weak point, or let us know something specific you're having trouble with.
Two general pieces of advice: use the Examine button on enemies, traps, etc.; and use everything in your inventory. For example, when I first started I didn't use seeds for anything other than making potions - realizing the offensive and defensive uses of seeds helped me out.
It gets a shield when stepping on a trap, so plan your movementa carefully
When in supercharged mode it moves more quickly, so you need a way to get some distance. Swiftthistle seed, Chains, Potion of Haste, Hourglass, etc. DM-300 moves more slowly through large passages, so use the center of the level to your advantage.
When in supercharged mode, the sparks might give you a hint about which way to go... Don't step on them though
When D-300 makes rocks fall, look carefully - there will always be a safe spot to move
Ive been pretty active in steaming my shattered pixel dungeon runs in twitch drop a follow and catch me online i can explain and give advice on everything in the chat. https://www.twitch.tv/draw_to_life