With loyalty greater than or equal to 60, you can persuade Betsy to masturbate in the tavern ("Just relax" option).
Yes, indeed ... there is a rather complicated system with thresholds, which definitely needs to be simplified or painted in more detail.
In general, here is the exact information - if Betsy has a corruption of 60 and higher, then when she jerks off to Gaston under the table, then her corruption can be pumped up to 70.