1. Thirty minutes
2. Of course she didn't get tomato sauce on it, because she is a careful, considerate child who appreciates the time and effort that go into making beautiful custom-made hand-knit garments.
3. Less than three minutes
If your answer was #3, then bing-bing-bing -- you are the winner!!! She was clearing her brother's plate from the table, and despite being warned to be careful
Thankfully, we whipped it off, blotted it, rinsed it with cool water (from the wrong side, so the tomato sauce came off the same place it went on), added a bit of detergent, rinsed clean, and oof -- it came clean. It has now been blotted with towels and is lying flat to dry again. This sweater will stay untouched by childish hands at least until I get the buttons sewn on and I take a few adorable photos.
After that, she can destroy it however she wants.
It looks really good on her. :-)