Leasehold property maintenance - neighbour dispute and absentee freeholder

[KDW]

HI, I'm looking for some advice regarding my shared leasehold Victorian property (semi-detached), with an absentee freeholder. *My downstairs neighbour has for the past 14 years (since I moved in) refused to undertake any property maintenance, and the Victorian building is urgently in need of some repairs and facade management. I would like to know whether there is any legal option to pursue here. The roof (i am on the top floor) has a little leak, and we have a crumbling front door - etc. The most trouble issue for me however is that she is a hoarder, the front garden is full of hundreds of plastic pots, the curtains of her house are black and crushed to the window with plastic bags on the other side - I would never be able to sell my property with it in this state as it presents so badly. Our relationship is not bad, but she does not see the problem and will not engage in making any improvements.* Her windowframes are crumbling and rotten. I have had mine repaired in the past couple of years but the house looks a state.* We have never had a freeholder, and I originally had some indemnity insurance put in place to secure the mortgage.* Does anyone have any advice on what I could do to force some action to improve the state of the property?