I'd think you need to add extra things to the existing PYTHONPATH or other variables, rather than add it standalone.
I.e. if the one you're adding is overriding the existing one set up by the install, it'd explain why other things stopped working.
If the original settings are lost, just repeat the Python install.
Then check the value of PYTHONPATH, whatever it is, append the location of the Meraki package, each path in the list is separated with a semicolon ;
If you type pip show meraki it'll tell you the install path.