Time to slip back into the house. You need to either get through the door before the guard gets in position or lure him away and slip in. If you are quick, even going around all the bushes, you can get around and through the door without any trouble. Running up from the left-hand side can also prove to be helpful as the guard could just let you in.
Most likely, approach the guard from the left, coming up from the far side of the pavilion.
Let the guard spot you and begin to approach you. Quickly turn around and head over to the left. Loop around the bush as the guard approaches your last known position. Just head into the house from there. You will see the girl just in front of you.