Break the window with some stones

As you can't get inside any other way, you grab some stones and throw them through the window. It shatters on the impact, but you must take great care while you try to get inside, not to cut yourself. It would be painful, but it would also leave blood marks in her house and a wound on you, so Sofia could quite easily identify who the thief was.

It takes some time to get yourself inside without any cuts. Once inside, you hear the mass is over, you have no time to stay there! You grab a bunch of keys (hopefully they will be the ones you are looking for) and open the door from the inside and get away.