This is a great question. Miss Maudie is a great character in the book, and a few different items represent her personality.
First, in several places, Scout says that Miss Maudie made the best cakes in the neighborhood. What makes this even more significant is that she make these cakes for the children. She does not find the children annoying, but she loves them and treats them with respect. Here is what the text says:
She made the best cakes in the neighborhood. When she was admitted into our confidence, every time she baked she made a big cake and three little ones, and she would call across the street: “Jem Finch, Scout Finch, Charles Baker Harris, come here!” Our promptness was always rewarded.
From this perspective, cakes would completely represent Miss Maudie.
Second, Miss Maudie loved to garden and she loves her azaleas most of all. Scout says that the children had free reign over her yard as long as they did not harm her azaleas. So, azaleas also represent her.
Finally, since she is a kind soul that does no one any wrong, she can also be seen as a mockingbird.