The only reason why this woman does this is because you all allow her to.
Go and get bags, fill them up with her shopping and give them back to her and tell her that she is taking the piss, throwing a person's lunch out is unacceptable and that as a result of her continues selfishness she won't be allowed more than her lunch in the fridge or it will be removed by anyone and everyone.
If she objects to that she can go and shop in her own time after work.
Stop putting up with this crap, go take the shopping out. She has no problem taking your sushi out and binning it.
Enough is enough. May the worms turn. 😎