................................................. Neighbours extractor fan vents into our garden

This has probably been mentioned before but i would like some advice please.

Our next door neighbour had problems with damp in her house she had extensive work done. She explained that her kitchen was very wet through condensation and would we mind having ventilation hole drilled through her brick extension wall into our patio area. My wife and i didn't feel there was a problem and was sympathetic. I think it was mentioned that a pipe would run from the wall our side and upward.

A builder arrived sometime after and a hole drilled nine foot above the ground four foot away from our back door. The hole was drilled from her side exiting into our patio.
An extractor cooker hood flexi kit was installed which vented onto our patio. The flaps are down in the closed position.

Every time my neighbour cooks a meal the flaps blow open and the strong smell of cooking and gas fumes blow around our patio. This rarely happens if my wife and i are in the garden.

We now own our house and spend more time gardening and playing with our 6 year old granddaughter. Sometimes these fumes would blow into our kitchen if our window was open during the warm weather.
i’ve been meaning to talk to the couple about it but we rarely see them. i’ve discovered she’s having treatment for cancer.

i feel conned that we are suffering air pollution so my neighbour could have a comfortable life and solve their condensation problem.

However, last year I unscrewed their outlet from our side of the wall and replacing it with a cowled outlet and screw it to the wall upside down so the fumes vent upwards.

There is still a cooking smell rises up if we have our bathroom window open.

I would like to fill the vent up altogether with expanding foam but should i inform her first. Or, should i seek legal advice as the smell and fumes is trespass onto our property?

Please advise.