Well yes, but only in the moment. They're supposed to allow play to continue and then flag during a break in play or a breakdown of the move. If that break in play happens to be a goal, then they flag after the goal is scored, which is what they did tonight. The goal happened almost instantly after the possible offside, so the flag went up instantly. If a marginal offside had been 20 seconds earlier in the build up to the goal, then she would have waited until the goal and then put her flag up for the offside 20 seconds earlier.