I'm largely okay with the player's ability to exploit monsters for Love. As to the beer situation, check around the school for an event that will cause Dianne to sell beer to her. (You may need to make use of Knaves' ability to disguise yourself as a certain person.)
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I certainly understand the disinterest in players farming love—I get the impression that combat isn't truly supposed to be a challenge, and Alouette's level doesn't really seem to matter anyway. Still, it is weird that said monster (the one that later becomes a slime Allouette) runs the love-dispensing check when denied a broken heart and indeed dispenses it.
As for the beer situation, I'd actually already completed that event when I asked the question, but didn't think to check whether that meant I could now buy alcohol. D'oh. Thanks for the help.