Right, she just tried to stop them like any prefect ought to. There was nothing to suggest that they were friends, or that they knew each other since before Hogwarts. I don't know where the Snape/Lily shippers got their suspicions, but it couldn't have been from Snape's Worst Memory!

Some friend. Even hiding a smile at his predicament. I'd sure not have a friend if I acted that way when my friend needed help. Instead, of course, Snape tried to hang on. It's pretty clear that she just used him for information and because he was the only WW child she knew - as soon as she met others, he was done for in her book.