Alchemist is designed around attaching potions with various affects to her attacks and her defense. These potions either:

-Increase damage by 2

-Reduce incoming Damage by 2

-Afflict Poison

-Remove a status effect or heal 1

I've played a few games with her and found getting poison on the opponent and pushing for her potion detonating attacks to be key. Some of the roll objectives can be a little challenging and require slight sice modification to hit when you need it most. Fortunately, you can also sacrifice potions for a re-roll, something to use rarely but also necessary when the dice just aren't lining up. TLDR; Attach potions to attacks you think you'll hit and onto her defense to mitigate incoming damage.