Lily has been portrayed as an intelligent and kind woman. She was one of the best witches in her year at Hogwarts. A combination of theses qualities may lead us to conclude that she must be aware of Snape's love for her but wanted to save him the embarrassment and pain and never acknowledged his feelings. She only wanted to be his friend.

Unlikely.

Lily and Snape were childhood friends, and had been friends up until they got to Hogwarts when Snape "fell in with the wrong crowd.

In Deathly Hallows, when Harry approached the Pensieve, he was grief-stricken and broken by battle. He practically fell into Snape’s memories, and discovered a little thin-faced boy who once knew a girl called Lily. Harry’s mother and Snape were childhood friends. Growing up in their tiny Muggle town of Cokeworth, they bonded over their magical powers like other kids do over toys.

Once at Hogwarts the two friends were sorted into different houses, and later Snape fell in with the wrong crowd. Not just the usual teenage reprobates, but future supporters of the most powerful Dark wizard of all time.

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_{The chapter that made us fall in love with… Severus Snape - Pottermore}

I doubt that Lily ever knew seeing as they were such close friends that had been just friends for many years. Here's some info I found over on Quora that seem quite relevant and helpful.

I don't think he ever did tell her, I don't see that in the books. Snape probably was like most teenaged boys-he couldn't bring himself to tell her how much he loved her either because he was shy, or thought he was unworthy of someone like Lily and was afraid of rejection.

I think Lily may have cared for him immensely, but there is no evidence that her feelings were as intense as his apparently were, or that those feelings translated to any kind of physical attraction or romance. Snape was an oddball as a young man, and while Lily cared a lot about him it may have been only as very good friends. Whatever chance Snape may have had with Lily died off when he started dabbling in the dark side of wizardry.

Lily couldn't deal with his slide toward the dark side, that slide changed the young man she thought she knew, and scared her. She was concerned about him, but at the same time, she knew that as long as he persisted in dabbling in the dark magic and hanging around those that did, she couldn't be with him. But she still cared about Snape, she would rebuke James when he and his friends would tease him.

Personally, I think she cared about him immensely till the day she died. They were close friends, she saw in him someone special that she could care about. But she couldn't be with him.

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_{Did Snape ever tell Lily that he loved her? Did she ever figure it out? - Quora}

So, it seems like it was very unlikely that Lily ever found out Snape loved her.