Parshas Emor - Rav Yehonoson Eibushitz - Why Is The Mother Not Disgraced?
"U'Bas Ish Kohein Ki Seichel Liznos Es Aviha Hi Michaleles", when the Kohen's daughter enters into a forbidden relationship she disgraces her father (Emor 21:9). Rav Yehonoson Eibushitz asks why only her father, what about her mother?
He answers that a Kohen is forbidden to marry any women who lacks a degree of Kedusha and is not perfectly pure. Therefore the roots of the evil within the offspring cannot be attributed to her mother, and her father is singled out for shame.
Alternatively he says the Kohanim are the ones who are supposed to warn Bnei Yisroel about Inyanei Kedusha and to avoid immorality. When her father gets up to speak about this, he will become a mockery as his own daughter has defiled herself. Her mother has no such issues.