She wouldn't be able to break into his house, not in this shape, not at this time of night. It would wake them up, and the gig would be over. It probably wouldn't be wise to change forms at this point - there's so much food inside her that the consequences could be dire.
So her revenge would be slow, piece by piece. It's dark out, so she slips out the back door of her house after tossing a dark blanket over her back and wearing it like a cloak as she slips out to his backyard.
Break the windows? Too noisy. Lawn furniture? Hmm... no, not yet. Perhaps later she will attend to that. But his garden... that was perfect. Despite the fact that she had gorged herself before, the sudden mass shift of turning from a woman with an udder to a pig-woman was too big to be sated fully on what she had eaten, and here was his garden, with its large cucumbers and ripe tomatoes and sweet red bell peppers... she salivates at the thought, and quickly begins to devour his garden, noshing and chomping at the plants voraciously.
It was large for a backyard garden, but it takes Mary fifteen minutes to devastate it. Was this all she would do to them? No, not by a long shot. But it's a nice start, and over time, he will learn the mistake he made by spurning her advances. She returns to her house and quickly locks all the doors and pulls all the shades down. Her home, her pigsty.