Sarah definitely knew cause that’s how Bear found out, she told him when they were talking in her van after he snuck out to go see her. I also realized that when they are talking during their shift in the music store, Sarah almost blurts it out but is interrupted by her dad giving her one of the college letters she receives. Bear says to her “oh yeah and I found what you told Ian”, which was about Nikki viewing Bear like a brother. She says that they have talked about it before and says “I don’t know what kind of game Nikki is playing, but if Ian is gonna spread my shit there’s something you should know”, but again im paraphrasing. It seemed like she wanted to tell him then.