Mineko's role in the anime is to be a comedy relief character, always being hyperactive, clumsy, and random. She is constantly jumping around, and tries her best to make people laugh. Making people laugh is like making up for her own depression.
However, her main role is representing how dangerous the Reborn Shadows are, and showing just how bad they can affect someone's mental health.
Her slowly deteriorating mental state is to show just how cruel Shadows are.
However, Okami has high hopes for her to be a good role model for those with severe depression, as Mineko hangs on even with all the things she has been through. She knows her tragic fate, and yet she desperately tries to stay positive.