A good friend never congratulated me on my engagement

A friend of mine who I've known for about 2 years didn't congratulate us on my engagement. Last year we took a trip just her and I to Key West for spring break. We've spent good times together. She's friends with both of us, my fiancé and I. Every time we went for drinks or dinner my fiancé always paid the bill. We were nothing but generous and kind with her. I just find it weird that she didn't give us a simple congratulations or show any emotion, but instead an "Oh" and an upset look on her face. I'm confused.