There is no such thing as a "connection TSA line" at SFO." Where you should clear depends on the concourse from which your domestic flight is departing.

1:40 should be sufficient, noting though that bags often take 45 minutes at SFO.
I would not recommend walking to T3 or T2 due to the construction. For an F departure, it's better to clear at G. For a D or E departure, AirTrain to T2. For T1, I would probably walk.

I'd walk to no matter where, and for anything but F and G now, probably walk across to A and see if there's much of a security line and probably enter there and walk airside the rest of the way. But can you please advise if the outdoor sidewalk (either upstairs or downstairs) is available to walk between T3 and T2?

A few weeks ago for an Alaska departure, I had a bag to check and a departure gate in Terminal 1, B-Concourse. I walked from BART toward Terminal 3. When I got there, things we're walled off. I'm not sure if there was a way to walk outside around it. No matter, as my plan was to do down into the parking garage and take that shortcut we locals know about. It worked like a charm. I don't think I'd recommend that to visitors, since there's a good chance someone unfamiliar with SFO would get lost.

For our friend, yes, I think the choice is either go through security at International-G if the departure gate in in G or F. Otherwise, go the other way with possible entrance at International-A, or Terminals 1 or 2. The appeal of International-A is it often has very short lines in the morning.

If one were determined to walk in that direction anyway, might as well scope out the length of the security line at Intl A, you can always walk A-B-C-D airside.

I've said this before (possibly in a different thread): While I'm a walker by nature, unless you're actively seeking to stretch your legs, the AirTrain is the way to go from International to T2. From the G side of the departures lobby it is one stop on the Red Line.

I also don't much care for either A or T1 security. I especially despise T1 as they have those awful new baggage scanners which back things up at both ends - loading your bags onto the belt and picking them up post-scanner.

As at 2 months ago, when you got to the point that was walled off you could walk outside for about 50 meters and then re-enter the terminal. Of course, with on-going construction it's very possible that's different now days...