ANSWER: Your question about female homosexuality and where does the Bible say it is a sin is mentioned in several scriptures. In Romans 1, the Apostle Paul stated that women who change their natural use just like men (verse 27) are in error or sin. God treats both males and females the same regarding this behavior (Romans 1:23 - 27).
Concerning this type of sexual behavior, Jude states that Sodom and Gomorrah gave themselves over to strange flesh that included both men and women. He said when God rained down fire and brimstone it was like being thrown into the Lake of Fire. It revealed how evil God looks upon this practice of sexual immorality and going after 'strange flesh.'
7. Just as Sodom and Gomorrah - and the cities surrounding them, in the same manner as them - having given themselves over to sexual debaucheries, and having gone after different flesh, are themselves exhibited as a perpetual example of undergoing the punishment of eternal fire (Jude 7, HBFV Translation)
However, what is more important than this practice being a sin is why God detests it and what is bad about it. In 1Corinthians 15 God says He is reproducing Himself by having sons. We are all to be God's sons in His family. What is bad about homosexuality is it is against God's purpose of creating sons for His family. You cannot produce children through this kind of behavior, and you certainly cannot do it through bestiality. In Leviticus 18 God says that committing bestiality causes the same kind of sexual confusion as same sex intercourse.
22 No man is to have sexual relations with another man . . . 23 No man or woman is to have sexual relations with an animal . . . (Leviticus 18:22 - 24)
Homosexuality of any variation is confusion according to the Bible because God ordained reproduction through kind after its kind (Genesis 1). These types of sexual practices are against God's way and His purpose. You can only produce children of kind after kind or between male and female. This is God's Law. Anything contrary to fulfilling God producing sons in His family is a sin!
In closing, although practicing homosexuality is a sin, ALL sin, if sincerely repented of, will be forgiven by God through Christ. Though some may feel otherwise, it is not the unpardonable sin and people do not fry in Hell for all eternity for deceivingly indulging in such behavior.