I have been involved as a therapist/counselor at a local clinic.
The way the clinic is set up is: Anyone can walk in off the street and we provide free counseling for them.
(The clinic and the clients are not Jewish)
The way the clinic is set up is that the space we meet clients is “downstairs” where there are 4 separate rooms (no locks on the doors).
What is a way that I would be able to counsel women without it posing a yichud shayla?
(At this point I generally leave the door open a small crack).
If people might walk in during a session (such as a secretary or a different practitioner), or at the very least knock on the door and walk in, it is permitted to close the door. You could also make an arrangement with others that they should walk in now an again without calling first.
However, if nobody would ever walk in during a session, and no arrangement is made, the best option is leaving a crack open as you are doing.