My Babysitter's a Vampire/Headscratchers

Erica and Rory are able to stay among humans with relative ease, despite being full-fleged vampires. Why is it that Sarah has implied that she isn't returning to join Benny and Ethan now that she's fully turned. Is she just scared that she won't be able to handle herself?
- Most likely, especially since she's had a taste of Ethan's blood which is supposed to be super rare blood type. she's probably afraid she'll lose control or she doesn't think she can face them.
- It didn't seem final, but so soon after she had broken her commitment to not drink human blood, she was probably just afraid to face him. She wasn't leaving them forever, she just wanted to give them/herself some space.
In Friday Night Fights, Sarah is ready to stake Kurt if her suspicions of Erica having turned him into a vampire were correct. She's ready to murder him for being what she is, but shows no interest in killing Erica, the vampire who turned him. (Well, WOULD have turned him, had the theory panned out) Definately a What the Hell Hero moment for me when watching it.
- The short answer to that question is that it's easy for her to contemplate killing someone she barely knows, but it's more difficult when it's her best friend.
In the Humans VS Vampires game, why are Sarah and Rory humans?
- They're not humans. They're just fighting for the human faction.