I actually used to think that hooking up meant making out but have found that most assume it to mean sex. I think age plays a role in it. ( i.e. If your 30 it is sex but 14 it means make out). I think as you said, it is supposed to be ambiguous because some people feel more comfortable with that. I used the term and my therapist asked me to clarify what that term meant to me I guess just to make sure we were on the same page.
So in short, your T probably assumes sex but if you feel it's important to distinguish you could just double check that she understood. Best of luck!