I promised I would update so here it is.
original thread
www.mumsnet.com/Talk/am_i_being_unreasonable/a1545014-to-be-a-little-suspicious-of-landlord-MIL
Readers digest version. MIL is our landlord, really rubbish one who breaks the law by not maintaining the boiler at all. We had a sort of agreement to buy this house from her when we could afford to but when we got to that point she kept putting off, making excuses.
We've bought a house, moving this weekend. When DH told MIL she had another screaming tantrum and could not believe what we're doing to her. She's currently not speaking to us.
MoreBeta nailed the situation in his first post of that thread. The mortgage on this house is large, none of the capital has been paid off and she did expect us to take on responsibility for her debts of which this house has seen absolutely no benefit from.