I am in the process of creating an asset for a character model, and when I try to use the Solidify tool to thicken the surface, I get a strange result where some faces thicken in the opposite direction, which messes up all the geometry. I've already looked at several tutorials and threads regarding similar topics, but nothing I am doing seems to be working. I've attached a couple screenshots and (will attach) the .blend file. I'm also fairly new to Blender, so I don't quite understand what I can do to fix these issues.
This is what the model looks like before the modifier.
This is what it looks like after.
My only theory as to why this is happening is that maybe the normals of those specific edges aren't aligned with everything else.