Most probably (i'd say 98%) the ORD flight will leave from B or C. Personally I would head to the spa in the South Lounge first to check for appointments, and if they have none, then get them to check (call) the B lounge. More often than not I get an appointment this way.

It's easy to walk from B back to A (in the unlikely even you get an appointment in B using the tunnel on -2. It takes less than 10 minutes (I made if from B lounge to Galleries South in 6 minutes once). From B to C you can also walk or use the shuttle. Either way, before sitting on a plane seat and eating/drinking for the next 8 hours, a short walk between A and B is hardly the worst idea in the world