Scheduling client sessions in such a way that no counselor is ever completely alone in the office with a client should be a priority. An alarm system with an audible alarm that dialed in to police dispatch would also be good. I don’t know what the privacy restrictions of the practice would require or limit with regards to video monitoring/recording. If visible cameras are an option, they should be purchased and installed. Maybe at least in the common areas and entrances/exits if they can’t be installed in the individual rooms in which the sessions take place.
Weapon wise, since guns aren’t an option for your wife right now, a concealed fixed blade knife and OC would be my preference were I in those circumstances. The only way I can think to conceal a fixed blade knife on-body in the kind of attire clinicians wear in such a way that it is accessible while seated would probably be a neck knife. Seated access is important because the client interaction aspect of the job is primarily performed while seated. With your wife being at this stage of pregnancy already, she’ll likely be slower getting up out of a seated position than she used to be.