She's only about 115-130 (assuming she gained the Shawl at a normal age 25-40). She says herself that she has only worn the shawl for 90 years. Certainly she's considerably older than Sheriam, but by AS standards she is still considered young. Siuan's discussions around proper Sitter Ages (wearing the Shawl at least 100 years) would put Galina on the young side for Sitter even now. And she was named Ajah head 18 years ago, which would have made her a very young Ajah Head... IMO she was likely already on the SC when the black chose to make sure she became Ajah Head as it seems unlikely they would put a rank and file member is a role such as this. Better to have one of their own placed here. Not be any means certain that she was already on it, but since she was #2 behind Alviarin it also seems likely that she had been sitting on the SC for a while.