It says in SA YD Siman 305 that a Bas Cohen that has a bechor (firstborn) with a non-Jew there is chiyuv of pidyon haben since the Bas Cohen through having relations with the non-Jew she looses her status of being a Bas Cohen. What about if a not-frum (irreligious) Bas Cohen before becoming a baalas teshuva (religious person) had relations with a non-Jew. Then after becoming frum (religious) later got married to a Yisrael and had a bechor. Is there a chiyuv of making a pidyon haben on that child? (My doubt is because through the relations with the non-Jew before becoming frum perhaps she lost her status of being a Bas Cohen.)
Kitzur Shulchan Aruch 134:9 clearly indicates that a Bas Kohain who has had relations with a non Jew prior to having a child with a Jew would do a Pidyon HaBen as the relationship is what makes her a Chalal.
Shach Yoreh Deah 305:22 also says that a Bas Kohain who has had relations with a non Jew prior to having a child with a Jew would do a Pidyon HaBen.
A kohen's daughter does not lose her status as a kohen's daughter by simply having pre-marital sex; she loses it through either marrying a non-kohen or through having his baby. In the event that she marries him and then has a divorce, so long as she was never pregnant she regains her former status and all of its privileges.