You probably don't want to use the system python with blender. The version of python that comes packaged with Blender has the python bindings for that version of blender (bpy) already installed. If you suddenly use the system python, blender is probably going to break if you want to install a different version, and definitely won't work if you want to use it with two different versions of blender (e.g. the stable release and the current beta release).
Instead, just take advantage of the fact that blender comes with its own Python distribution: it has its own version of pip. It's also a good thing, because it isolates the python installation between different versions of blender. Here's what I usually do to install modules into Blender's python. From Blender's scripting tab:
import sys, subprocess
subprocess.call([sys.executable, '-m', 'pip', 'install', 'pymesh'])
What this does is call the pip associated with the current installation of Blender, and tells it to install pymesh.
You might need to run blender with elevated privileges (e.g. run as administrator in windows) for this to work. You also might want to delete the install of pymesh that you've already placed in your blender python folder.