I'd absolutely talk to my T about that. The most appropriate and professional way for a T to handle such contacts is not to respond at all and then tell the client about what happened. While "thanks" does not imply anything specific, it's a slippery slope for a T to respond to such contacts in any way. If she had said anything in addition to "thanks", this could be construed as a violation of confidentiality depending on what she'd said. It's illegal for a T to even acknowledge that So-and-So is their client unless it's a situation when they are required to do so by law. Also, while therapists are not legally or ethically obligated to tell the clients when receive a communication from someone about the client, in most cases, it's a bad practice not to do so. Of course, different therapists have different opinions about it, and, of course, the decisions are made based on the specific circumstances, but I can't think of many situations when I, as a therapist, would not tell the client that I've been contacted by their family member and, as a client, I would be very pissed off if my T didn't inform me about such contacts.