Quoting ♥teaspoon♥:“ My son is 8 months and started that a few days ago....he smiles and will laugh when I do it back though....I ... [snip!] ... though....I probably wouldnt worry...they make lots of weird sounds. Its when they stop making sounds I think we have to worry.”
She was around grandpa recently so she could have picked it up from him! I'm glad it is normal. Last time she learned to fake cough she would laugh after so I knew it was fake. With this she just keeps doing what she is doing when she makes the sound. I couldn't tell if it was fake or not but i'm glad it's just something new and fun for her!