unconfirmed smell from the airing cupboard???

Tenancy Types and Management

hi, about six months ago, my tenants contacted me saying there was a really bad cooking smell coming from the airing cupboard in the front bedroom (semi detached house) and recently next door had had some work done to put a new kitchen in and they had moved the kitchen to the party wall and the kitchen extractor was now on that wall, but this smell was very intimitant, i went to see the neigbours who have being trying to help as much as possible, but no one could understand where is was coming from. i did not hear anymore from the tenant for about a month, then she said she can not bear the smell, in the bedroom and had to move all her bedding and clothes from the airing cupboard, again i went next door anyway this time i went to enviromental health, to log it, but they said as it was a cooking smell and it was intermitant, there was no legistation to cover it and was not seen as a nuisance. so i went back and explained this to the tenant and suggested that as no one had smelt this smell apart from them that when it happened to contact next door to get them to see what was happening and to see if it only happened when the extractor was on, well to cut a very long story short, the tenant has turned into the tenant from hell, and for the last 6 months as been verbally abusing the people next door and the neighbours beyond that, and also threating me with legal action as they are not getting enjoyment out of the property, but still no one else has smelt this smell, we have offered as soon as it happens to let us know and we would come round, anyhow, she wants to leave, not a problem, apart from she has paid a year up front , but i said once we relet i will refund her for those months, the neigbours have also had enough and called the police and council about her as she had been screaming at them from her window etc so it is logged with them to so know we have a situation where we now have new tenants wanting to get in, i have got a building surveyor coming round to inspect the party wall for any problems and if found the neigbours will pay for that if nothing is found i am left with and additional 400 bill, she was also informed by the envir depart that it was nothing they could do, so now she is claiming breach of contract as the alarm in the house that never worked and we offered to get replaced and she did not want one, now wants it as its my duty as a landlord apparently or otherwise we are in breach, which as far as i can see we are not, as there is nothing in the lease to say we were going to supply on, only if there is one she should set it, so it has been a nightmare, as this is a rental not for business but just to pay the mortgage as i moved in with my partner it has almost put me off renting and just selling it would be a better option, but we have decided to give one more set of tenants a go and hopefully my current tenant who has been terrorising the neiboughs will just go away soon, but she is still threating to sue, for what i am not sure.
has anyone experienced anything like this, as she has driven me up the wall and all the way around it!