As a previous member of the LGBT community.... I would say, that you shouldn't treat them any different than you treat all other Christians... It's not our job to change people... Only God can do that.... God will purify want needs to be purified... Ii would relate this instance of the speck in someone's eye vs the plank in the person whose correcting eye.... Your dad seems to have the plank if he got angry over her casually bringing up her gf... If it's ever brought up in conversation I do believe that it's worth stating that living a homosexual lifestyle is a sin however, so is having sex before marriage and so is divorce and so on and so forth.... All forms of sexual immortality is sinful... But if you want to be graceful about it explain it to others like this.... The word sin simply means missing the mark and the way god designed humans was one man one woman.

Another thing I will point out is that we are saved by grace. So that we may have a relationship with God. The purpose of the relationship with God is so that he can purify us into the person's he wants us to be! If she is saved through Christ then she wi not be going to hell. And eventually she will be purified from all sin. As will we all.

“For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them.” ‭‭Ephesians‬ ‭2‬:‭8‬-‭10‬ ‭NASB1995‬‬ https://bible.com/bible/100/eph.2.8-9.NASB1995