Depends what you want.
In Roya, everything has a cost: the obvious cost is money (some skills, learned from friends, are free), but as you saw, some things instead cost corruption points. Removing the collar costs 4 corruption points; doing a lewd action costs only 1 corruption point (that's 75% less corruption). Even learning a «free» skill like Fire 1 from Charlotte has a cost: since it ends the day, and since corruption increases by 1 every second day, this means that every day-ending action costs one half (0.5) corruption point.
Of course, if your intention is to keep Aura pure and prude, then this precludes lewd actions; but if your Aura is a pragmatic, then she can sometimes use lewd actions on those days when the curse starts to affect her stats, in order to «reset» the curse. Sure, you'll accumulate corruption points this way, but at a much slower rate than if you used the Star Knightess, and it'll be only half a corruption point more that a non-lewd day-ending action...
So you have a choice: reset the curse with very expensive (in monetary terms) Blessed Water, or with moderately expensive (corruption-wise) lewd actions.
To win hard battles without relying on Star Knightess, at the start of the game: you can always use bombs. Sure, bombs cost money (50 Gold) –– it's up to you to decide which is the more expensive, either spending 50$ per bomb or 4 corruption points for removing the collar. There's no definitive answer, it all depends on your evaluation, on what you want.
My suggestion: just enjoy the game, without trying for a perfect score. Once you've beaten it, then you can restart it and aim for perfection or purity.
