Yikes!
Do you honestly think she doesn't know any better? I guess if you really think she is this clueless you could always strike up a conversation about how you know it's early, but you are so excited to start solids when your baby turns 4-6 months because after all you aren't supposed to give anything but BM or formula before then.
I'm guessing she knows and just doesn't care, thinks it's funny, or has found that's a way to soothe her baby. If you suspect she already knows better, then I guess there's really nothing to be said or done.