So I've got the chance to play the game a second time with pure love route (Not even a touch from the prince), it works, what you have to do is carefully manage her stamina, my strategy is help her in the morning, work at the evening. You also have to beware with your money, each day she'll use 15 of her stamina and you need her stamina up to 30 each day so the prince won't have the chance to touch her, close the store when necessary, usually you'll need a can or 2 energy drinks which cost 500-1000, which can be costly, see which way is suit your situation.
Something I must say, I keep letting Aldair make love with Lisa until the travel event, by then the body-match point is around 360, that took some times, but one trust of the prince equal the amount of the time we've spent, so holy shit, do not let the prince come any closer to Lisa, otherwise? Once you go big, you never go back, took me a helllotta time to match the body back.