He definitely is reading her right. Joan will often take cases that would bore Sherlock, just to help someone who's in trouble.

"For about seven years," she answers. "Although I wasn't a detective when we started working together. I was a sober companion."

Sherlock has long released her from her obligation of confidentiality regarding how they first worked together. She usually wouldn't talk about it regardless, but either this is a dream or she's trapped in some weird extradimensional reality. Either way, she feels less obligated to avoid the subject.