I agree, a friendly conversation, with the sensitivity that she may not immediately like the idea of $$$ work, is a good start, and with "I could get you some names to call' as a possible offer if the conversation seem's headed to 'I have no idea who to call"
A real arborist, not a tree cutter downer. There's one who's advertised in Baltimore for years...Bartletts?
I wouldn't stay up all night worrying, but good to keep an eye on.
We have an oak that suffered a lot of leaf loss over a dozen years ago, it's still chugging along, it's a pin oak so it does not have the big lateral branches of some other oaks (can't quite judge what you've got there)
