Summer Van Horne is a welcomed member of the Rock and is a generous woman played by Candace Cameron Bure.
In Season 1, you see her as Steve Tanner's 'secretary'/girlfriend. They seem to have a close relationship but in the first episode, it is said that they are hiding their secret affair from Steve's daughter, Lauren. It is revealed to Lauren in episode two when, while Steve and Summer are in their new office and intimately hugging, Lauren spots them in the act and shouts out, "You're banging your secretary?!"
After being exposed, Summer tries to get closer to Lauren, despite the lack of Lauren's interest. Then, in the episode 'Like mother, like daughter', Summer reveals the secret about her high school life and how she was known as something along the lines of the class slut. Lauren initially uses this against Summer, but when Lauren is left friendless and in a crisis, Lauren turns to Summer and the two become close.
By the last episode of Season 1, at nationals, Summer discovers that Steve lied about the truth of Lauren's mom. In a few episodes back, she believed that Lauren's mom was a charity worker until Steve revealed that she was addicted to drugs. Lauren invites her mom to see her at nationals, but her mom is a no show. Summer takes it into her own hands and decides to ring Lauren's mom and ask her why she's not there. She was told that Steve threatened her if she came. This hurt Summer and she immediately broke up with Steve, but stayed for Lauren.
During Season 2, Summer starts a relationship with Rock coach Sasha Belov. Before a certain episode, Sasha seemed to constantly flirt with Summer saying how she had feelings for him. When the bingo episode came, Summer goes to visit Sasha at his home to ask about China's invitational. When he says that they are coming, they hug and straight after, they kiss.
Summer and Sasha decide to hide their relationship for the gym, especially Lauren. But in the last episode of Season 2, when Summer kisses Sasha, he stops her from going too far and says that he didn't want to affect her values and breaks up with her.
At the beginning and during Season 3, you see that Summer gets back with Steve and seems to stay there with Lauren begging both of them to marry. Near the end of Season 3 and at the last episode, Summer finds out that it was Lauren who revealed the tape of Sasha and Payson kissing to Ellen Beals and says that she wants nothing to do with the family at all.
The next time you see her isn't until middle Season 4, while Lauren is in hospital with her condition. Summer recommends prayer to Lauren as she believes that it will bring her peace. She rejects the idea but you see her praying in later episodes. Finally, at the last episode, you see Summer and Sasha sitting together on a bench alone and they discuss about their life at the Rock. While discussing mistakes, Sasha says he regrets losing Summer and they kiss and Sasha says, "Don't tell me you stopped believing in miracles". This indicates they continued with their relationship, even with no further seasons.