First off, the "confidentiality" doesn't apply for doctor to doctor discussions. It falls under "professional confidentiality" where they agree to discuss a patient only between themselves at that time, and not share it with outsiders. So your professional sister COULD impose upon any T you find, to share. That is something you MUST insist your new T NOT do!

Now, all Ts do NOT know all other Ts. Plus, psychologists don't hang in the same grouping as psychiatrists...they are two different fields. Psychologists usually only have acquaintance with psychiatrists who have agreed to help on cases where meds are needed... but that's about it. To think your sister knows all of them is a misnomer, ok?

You can ask when you interview them, if they know her. (They might know OF her, and that's it, but odds are... unless she is a famous author or director in the area, nah they won't know her.)

I think it's good that you find a T for yourself.