The final 5 minutes of "You Are So Beautiful", where Tia and Tamera wonder who their birth mother was. Her name is Racelle Gavin, and she spray-painted a huge mural on a wall.
How about the entire episode is this? Throughout the episode, Lisa was focused on what she wanted for her birthday, and then saw how much Tia and Tamera wanted to know who their birth mother was, or how she looked like. She ends up being the one to finding the spray painted mural at the end.
How about near the end, Lisa goes to Tia's bedroom and watches her sleep, before giving her a loving kiss goodnight. While she felt a but heartbroken and feeling like she isn't a good enough mom for her daughter, she still loves her so much...
The song that plays during the scene, as well as the when the mural is found and in the ending credits fits well.
The episode where the girls finally meet their father, who is white, where they (although one of them takes time to accept it..) accept him for who he is, regardless of his race.