The smile that she gets when he tells her that she's a constant in Oliver's Arrow life is something that can only be described as wistful. Even if she's not necessarily needed, she's wanted. That means a lot to her.
"It's nice to know that there's some kind of constant in my life; even with all the bad that's supposed to happen." It hasn't been very long chronologically, but being with Team Arrow, being with Oliver and Diggle has become so incredibly important in her life.