Starting from day 16, please describe: her assigned rules, her aura on each day, and happens each day.
+5 to -2 in 4 days. It sounds like she became spoiled and may have lost some of her taming.
Losing taming can happen over time if her aura is stronger than the master's.
As for pride, rules like behave humility, pet and silence will be followed without forcing if her obedience is high enough. Deny toileting is also effective but may need to be forced. Forcing rules can cause despair, however, so is best done sparingly. Training her as a pet, pony or cow also lowers pride.
She can be trained in sex lessons (e.g. start with kissing, seduction) even while she is arrogant.
You can reach C+ rank with minimal training in a variety of sex skills, and reaching D- in a sex skill requires only one lesson.
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