A very difficult neighbour to my rental, complains all the time, now about noise from boiler

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Since I bought this property five months ago the neighbouring woman has complained unceasingly. first about the noise of small renovations during office hours, then about the noise of the new and very efficient boiler, then about noise from the new (single and quiet) male tenant. I have today received a letter from my local council asking me to have a gasman look at the boiler. The boiler (brand new and obviously tested as sound)is fine. The tenant is fine. She is just, frankly, a bit of a difficult person. She should have bought the bloomin' house herself. I shall invite the Council to install their noise-ometer when I speak to them on Monday, but have I any reasonable defence against her constant complaints? She is upsetting the tenant. I had the boiler re-mounted on rubber fittings at my expense when she first said she could hear it. And I have ensured that the boiler is not on during the night. I do honestly believe that the timid tenant is a quiet soul, and he is aware of the contractual obligation to be very quiet between 11pm and 7am. She is, quite frankly, harassing me. Can I get some sort of restraining order? I have made a written record of all her complaining, and kept the texts also.