I think its unusual for an OC to hire a lawyer to represent them. Perhaps the lawyer is hired to provide legal opinion to the OC and it will be represented by a committee member or the strata manager.
Remember that mediation is NOT about determining who is legally correct. Its a process for two parties to come to a mutually acceptable resolution. If the OC wants to lawyer up, then they would be better to save their time and money; refuse mediation and go directly to NCAT
At mediation, the lawyer cant make agreements on behalf of the OC unless instructed at the mediation by either the strata manager or a committee member.
You may also want to look at S103 of the Act. Hiring of lawyers needs approval of the OC, unless its an emergency or the bill will be less than $10000.
You can find out all this stuff by asking for the lawyers cost agreement with the OC (lawyers must provide this at the start of the engagement in order to be paid) Its NOT a legally priviledged document and as an owner you can access it as its a record of the OC.