It's wrong to make assumptions without evidence.
Jane discovered that someone has eaten the sandwich she left on the kitchen counter for herself, with suspects including her dog and her roommate.
Jane wants to eat a sandwich.
Jane sees mustard surrounding the outer parts of her dog's mouth, realizes he was the culprit, and makes a replacement sandwich for herself.
Jane accuses her roommate of taking her food, as he has done once before, and eats a sandwich he was keeping in his fridge.
Jane is more aware and does not leave her food unattended in the future.
Jane's relationship with her roommate continues to become strained and awkward.