I have read all of the thread
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I agree that intergenerational living can be difficult; but that's not the whole story here. It started as a story about a daughter who was being unreasonable about a shower, then we found that the OP wanted to change her arrangements from an occasional visit to half of the year, and wanted her daughter, who had been renting the flat from her, to move out, or make way for the OP and her partner.
Yes, it would cost a lot to rent in London at full price, and yes, the OP has paid the mortgage, like any other landlord. But if that is to be taken into account, what about the profit that has been made on London property for so long, that makes it impossible for young people to rent unless they have a high income. It's a 'boomer/millenial' parable, really.
It's neither the OP's, nor the daughter's fault that London rents are so high; but unless the daughter was told clearly at the start of the arrangement that she was basically a house-sitter, and could be evicted if her mother's circumstances changed, then I can understand her feelings about the visits.
As it is, Brexit looks likely to make it necessary for the OP to spend a lot more time in the flat; so the honest thing would be to explain that to her daughter, and mutually agree a solution. Making her feel that she is being asked to leave because she has been unreasonable doesn't seem fair, and verges on gaslighting.