She's an attorney -- such audit/evidence trails are essential in her profession.
Email clients don't have to honor read receipts. In fact, apps such as Outlook, have an option where you can turn it off. And I've use a Lotus Notes macro that removed them.
Yea, and I doubt that the footers lawyers append to every email mean much in terms of disclosure, but that doesn't stop law firms from trying it anyway.
I think read receipts fall into the category of "good faith effort", and not much more.