My 2cents on this -don’t know if it varies state to state, IME as a retired healthcare provider and divorce court user:
To set up a ‘my chart’ type acct, a code is usually given to the patient after appt for them to log on and set up username and password. Even if FD had known her Dr, he couldn’t go on and create acct just so he could view her info. However, since we know JD was going to unknown appts that morning, as I said before, she may have been carrying a medical file with her. If FD nabbed it out of her car, and that code was on paperwork, then he could have very easily set up an acct for her.
On EOBs: they are ONLY mailed to titled insurance holder. Ie, if FD were carrying insurance for the family, he would get EOBs. Even in a divorce, this holds. But IIRC, FD was not carrying insurance for the family. Therefore, any EOBs for in’s JD had purchased would go directly to her. MOO
Edit: now that I’m thinking more about this, I wonder if LE has checked her medical online accounts to see when and from what device they were set up. Seems too obvious. They must have.....