Boundaries changed

Hello
I have a private entry road shared with four terraced  properties which is the main entrance to my house, one of the properties is a gable ended, and has had a Garage built without planning permission. This is over 20 years ago but I want to improve the tarmac and the flag the rear of the terraces to make it look a lot better and becomes an extra area for the terraced owners to enjoy in the sun. The lady of the end house is refusing to give anything towards the works has the rest agree it needs to be done and I am the main area owner and I have insisted I will pay more to the improvements.
The answer I need to know is due to the Garage being built without planning has now changed her exit out the rear of the house, and now comes out on the gable end side of the house. Has her boundary been changed at the rear, has she lost it? 
The lady is holding up the works saying she  cant afford to contribute but seeking legal advice against the works being carried out, but the other three houses which everyone else agrees  to and prices agreed to, 
Please can you advise ?
Kind Regards
Lee
 

Hello Lee - we can't offer any advice and would steer you to also seeking legal assistance/advice as required.
We can provide registered information re the registered title(s) involved. So for her property/title, assuming it is registered, the title plan would confirm the general boundaries/extent whilst the register would confirm ownership and any rights/easements for example - you can check the registered information online and then seek legal advice as appropriate
If you are looking for wider comments online then other public forums such as Garden Law and Money Saving Expert often discuss such issues but you'd need to be clear re what's register/what's not. 
However the best advice I can give is to speak to a conveyancer yourself once you have all the relevant information