Is my friend flirting with my boyfriend?

This will be somewhat long, but I really need opinions, so please read carefully and tell me what you think! There’s this girl I know (Samantha) I guess you could say she’s my friend, but I don’t know her very well, and neither does my boyfriend. She invited me and my boyfriend to her birthday party. We went, I got her a necklace, my sister got her earrings, and my boyfriend got her an iTunes card. She thanked us all in person for the gifts, and when she got the iTunes card, she looked at my boyfriend and said, “Oh my gosh. I LOVE you!” I found it odd for her to say that, but didn’t think too much of it. The next day, my boyfriend texted me and told me that Samantha had sent him a message on facebook, saying “thanks for the sexy gift ”. Again, I didn’t think much of it at first, since people sometimes refer to random objects as “sexy” for no reason. But then I became more concerned, since he seemed very upset about it, and she hadn’t sent me or my sister a thank you message, just him. And as I said before, she knows my sister and I way better than she knows him. AND she put a winking face in the message… I need to mention, she has a boyfriend. And she acts very friendly with some of her close guy friends, letting them tickle her and pick her up. I’ve always been a little suspicious of her, sometimes she’ll just say hi to me, and then walk over to my boyfriend and poke him in the stomach or the face, and giggle a lot while doing so. My poor boyfriend is getting very creeped out by her. What is she doing? Is she flirting with him on purpose or does she not really realize what she’s doing? Whatever it is, I think she’s acting out of line. Please let me know your opinions, thanks!