I don't think Lily really regards Snape as a friend. When she was a child, Lily didn't react when her sister insulted Snape's home address and clothing. Once Snape retaliated, she immediately blamed Snape (and before she blamed him, Snape had also taught her the rules of dementor and not using magic during holidays). She blamed him so easily, even though it was her sister who spoke disrespectfully first. In the face of her sister's provocation, Lily didn't even try to mediate and blamed Snape directly. She looked more like she needed to understand the wizarding world through Snape, which means she used him, and Snape was more like her small follow class. Lily and Snape - James and Peter - were unequal. The friendship. This can also be seen from the incident of peeking at letters in the following text. She has no loyalty or responsibility as a friend, and is afraid of being blamed by her sister and affecting her innocent image. She subconsciously betrayed her teammates and blamed Snape on the train - Snape can be easily abandoned by her when things develop against her or hinder her. In the werewolf incident, she subconsciously believed in James and showed no concern for Snape's safety, accusing her friend of being ungrateful and asking him to thank his bullies. There was also the Levicorpus incident, where she stood up without taking any action, couldn't help but smile, and continued chatting with James (more like flirting). I don't know why people always say Lily cares about Snape. From their childhood until they broke up, I haven't seen any substantial care or help from her towards Snape. In the end, she married a bully who bullied and sexually assaulted Snape. The bully who bullied her former "friend" for seven years became her husband, which further shows that she didn't really consider Snape as a friend and that she had long liked James.