You don't have to cheat but if you're underprepared you'll have problems. Buy a Fire Ring from the shop before doing the quest, it'll massively reduce the magic damage since all she uses is fire. You might also consider dumping ki (use the Ki Orb important item) into Magic Defense and Attack; if you want a ton of ki you can lose to h-enemies on purpose. Also, if you lose the first fight (where she has the ninjas) you'll get the "I can't die here" thing and gain a level automatically every time you die, so instead of grinding you could just lose over and over. The one-on-one is a Game Over if you lose, but with +100 Magic Defense from ki and a Fire Ring her attacks in the second fight literally didn't do any damage. Charge up to 100 TP and one-shot her.
Also, actually use the familiars because of situations like this where they're forced, and bear in mind you can equip familiars with gear. If they fall behind in levels they're not even good as meatshields. They don't seem to have any use for TP (except the fairy's buffs) so they're best built up as mages. Petrification is OP and locks enemies down forever and Mass Drain/Sacrifice does a lot of unresistable percentage-based damage. There's no reason not to have a full party and familiars automatically have an accessory that doubles XP gain.
Seriously though, intentionally losing to the h-enemies is the secret to proper grinding. Every defeat leads to a pregnancy (plus a ton of other things because getting captured seems to always involve basically every non-lesbian sex act) and the titles from giving birth grant extra attacks (at least to the main character and archer lady); just one pregnancy lets you attack twice which is OP (you gain TP twice too), and I think 10 births (which is admittedly a lot since you have to rescue allies) grants two extra attacks for both the main character and archer. The critical boosts from having sex in general also help but only the main character seems to get +50% crit and that's from a huge number so I think the extra attacks are better to gain TP faster and double/triple your damage consistently.
Also if you don't want to actually get captured by h-enemies just equip anything that blocks Arousal on non-familiars; enemies can't engage h-combat stuff if the character isn't Aroused, even if they're naked, so they'll just tear everyone's clothes off and then waste their time trying to initiate scenes that will never trigger. Familiars also help spread out the targeting for h-attacks and familiars can't become Aroused but they do seem to take normal damage from those attacks.