I think my friend doesn't like the other people I hang out with..?

Ok, so we'll call my friend Shawnee. I met Shawnee this summer before 7th grade and we became really close friends over the school year. I have another friend, Sierrah. Well, one day I decided to sit with Sierrah and her group(they're all my friends too) at lunch. Shawnee came up to my locker after lunch and said "Why did you dit with THEM?" I don't think Shawnee likes Sierrah and her group, but I don't like some of Shawnee's friends either. What can I do about the tension between me and Shawnee?