Being that this is a spell quest. You can't have anyone help you. However I encounter the same problem. I've invested into using henchman, it is the same as asking for help from another wizard. The asking price for crowns in the shop is not expensive for one or two to help you through to defeat her.
Keep the drains small and expect to reshuffle. I actually had to reshuffle twice against her.
Don't hire henchmen. If you need a henchman on a spell quest, you're not ready to learn the spell.
If you keep going in and dying despite your best efforts, go down the following checklist before trying again.
--What am I dying to? Could I do something to avoid that spell or nerf it?
--Look at deck. What cards am I discarding, what cards am I always using, what cards do I always find myself wishing I'd put in? How consistently can I draw and enchant a rank 8 spell on turn 4? How consistently can I heal? Can I potentially shield EVERY TURN until I'm ready to start blading and hitting? Do I need to reshuffle?
--Look at sideboard. How many of my sideboard cards am I using? Which ones?
--Look at sideboard again. Are there any tc spells I might find extremely helpful for this one particular boss? Shatter, feint, dispels, Infection, Reshuffle, Cleanse Charm, Prisms, pre-enchanted Efreets or DoT hits in my school - many of these are low pip solutions to thorny problems.
--Gear and pet check. Waterworks or reasonable crafted alternative. Pet that boosts health, resistances, or may cast healing spells. Try aiming for minimum 70-100 critical block, 10-12% global resist, 300-500 max health boost, at least 90% in-school accuracy, at least 65% power pip chance, and at least 30% in-school damage boost. Having an incoming healing boost is also very helpful, more so if your pet has fairy or sprite.
Most people do the one hit AoE strategy. What I did on my fire: -3 blades minimum -2 or more feints on the boss -Vengeance/Amplify -Bubble -Colossal Meteor Strike wit 50%+ damage boost. That got me through that one!