Leaving unwanted furniture for the dirt truck to pick up

My mother complained that the bags that people put next to a tree on our road gets collected quickly and that we are needlessly keeping unwanted furniture etc. in our house when it can get collected quickly and for free. She threw some of our bags in that area.

I told her fly-tipping is wrong but she says that everyone does it. Fly-tipping is considered illegal and finable. I’m worried that she may be sinning by doing so. Does she have to repent? I’m also worried that I may have aided her as she asked for a bag to collect the waste to throw out and I reluctantly gave her.