My neighbor came over to help me with the TV and brought his dog?

Now she LOVES me, always has. But for some reason when I picked her up she was all tense, and my friend tried to pet her and she snarled at her, then tried to bit me! So I pushed her off my lap (gently, I didn't hurt her) and she stayed away from me, which is also odd behavior for her. She's about seven years old, has never done this before, I saw her a few days ago and she was all over me with snuggles and kisses. What was wrong with her tonight?