Bride left fuming after sister-in-law eats her dinner at her wedding.

There are so many parts to a wedding day that you look forward to. Of course, there's the actual ceremony, the after-party, and one of the most important aspects of the dinner.
However, one bride didn't get to enjoy her meal as her sister-in-law ate it while she went to the toilet. The bride explained that she needed to go toilet in the middle of dinner, and had only taken a few bites from her plate.
"My best friend and bridesmaid came with me (big awkward wedding dress!) and we ended up chatting in the bathroom for roughly 8 minutes about how the ceremony had gone etc before heading back to the room. Walked in, saw my SIL sat in my seat next to my new husband, though it was a bit cheeky but fair enough, I'd left him for a bit eating his meal."Approached the table, to find my SIL had FINISHED OFF MY PLATE???!!! I didn't know what to do except standing there a bit shell shocked! She apologised for been sat in my seat (didn't mention the food) and started to walk off, well my jaw must have been on the floor."I stopped her and asked her if she'd eaten my food and in her words 'yes, I figured you'd had enough as you're dieting and you walked off and left it'. I was speechless, she stood there with a smug look on her face, my husband's sat there looking sheepish, I explained to her I'd simply gone to the toilet and she said 'oh sorry, well there's still dessert I guess' and walked off!"Asked my husband why the hell he let her sit there and eat my food and he turns bright red and said he thought I'd finished too. Great. Fuming. Didn't want to kick off on my wedding day and make a scene so sat back down in front of my empty plate, looking longingly around the room at the people eating slowly who hadn't yet finished and pretended everything was OK."

Many replied to the post and were equally as shocked as the bride was.

One said:
"I'm astounded! That's taking CF to a new level.

"1. Who the hell eats someone else's meal unless they have been told they can finish it?

"2. Who the hell does that at a wedding? This isn't finishing a plate of chips at Weatherspoon's!

"3. Who the hell does that to the bride?!?"While another wrote:"No YANBU and I can’t believe she wasn’t embarrassed at all. That’s so awful."

What would you do in this situation?