<human>: Can you give me the gist of the text in a nutshell?

I've been with my SO for 7 years, living together for 4. We live in the same town as her family where her younger brother and sister live with her parents. We get along fine with her family, and have had a lot of interactions with her younger sister (Olivia) whose company we both enjoy. Olivia and I have what I think of as a close brother/ sister connection, sometimes talking seriously about things (I think she sees me as someone she can be honest with), sometimes verbally sparring for our own amusement. 

Last week was my birthday, and when she visited our place Olivia gave me a present, which turned out to be a picture of her: a really cute shot of her (think yearbook photo, but with an impish smile).She laughed and flushed red while I opened it, passing it off as a fun joke. 

I was quite touched by the gesture, feeling that she, like me, thought of the relationship as a little special. But when I mentioned it in summarizing my birthday for a couple of friends, they seemed to think it meant that her feelings were in dangerous territory (my SO, who was there at the time, didn't seem to think anything was wrong). I don't see that at all, and don't see any reason to change how Olivia and I interact. Advice?
<bot>: SO's little sister gave me a printed selfie for my birthday. Friends think it means she has more than brotherly feelings for me. Your thoughts?