Taking advantage of how easily she and Marla were able to blend into the background, Rita had stealthily activated her Succubus bloodline, and the mere proximity between her and the entire territory that seemed saturated with holy energy was... Sickening.
She had not felt that way with Melinda and was willing to bet it was because she was close to those even stronger than her, in who the bloodline was far more showy.
The reaction of course was not uncontrollable and was mostly so heavy because she could not permit herself to react to it and was forced to hold it all down.
However, it proved to Hal that bloodline-wise, Rita was at the equivalent of his previous lesser devil form and was a tad bit unstable.
The only way to curb such a reaction would be for him to advance his own bloodline and thereby advance hers.