1) Bob can decrypt the message by multiplying the encrypted message by the inverse of the 3x3 matrix that his friend gave him, if it exists.
2)Yes she can! Reason being that this is a linear system in which input $ X $ yields output $ Y $ and input $ \bar{X} $ yields output $ \bar{Y} $.
Therefore, $ a*X + b*\bar{X} \to a*Y + b*\bar{Y} $ where $ a, b \in \mathbb{C} $
