Actually, she means you (singular) are both (1) stronger and (2) happier. I apologize; I can see how that might not be clear. I'll play with my wording a bit more once the lyrics are officially printed.

I think she's talking about not only that, but also about losing her longtime friend to suicide, her X-year long relationship with Tomoya, and maybe even her #1 streak. The past year was really rough on Ayu; she lost a lot of long-lasting things. I can see how these lyrics can apply to any of these things, which is probably why it's called something as all-encompassing as "Life".