Hello and thanks for using Just Answer.
I am Al and am happy to assist you with your enquiry.
Unless your neighbour pays off her Mortgage, I'm afraid there is no way that you will be able to legally have the land registered to you. This is because, with all mortgaged land, no transfer or sale of part of it can take place without the Mortgage Lender's consent. Without this consent, the Land Registry will not register the Transfer of the land to you.
As long as a suitable Plan has been drawn up, which appears to have alreaby been done, most Lenders would grant consent as long as it does not materially affect the value of your neighbour's property. I really don't know why your neighbour's Solicitor had a problem obtaining this- most Lenders are approachable and are under a duty to correspond with us Solicitors.
If the above is not possible, the only other thing you can do is to go ahead and encompass the land into your garden by moving your fence. I must say this would not be an ideal scenario, as you wouldn't legally own the land until the period of 10 years has expired and at which point you would have to apply for "possessory title" of the land at the Land Registry. Therefore if you were to sell your property in the next 10 years, you are likely to face a problem in that your Buyers Solicitor would want you legally acquire the land, so you would be back to square one.
I would therefore suggest that you perhaps offer to pay your neighbour a sweetener to get the job done correctly and to perhaps instruct another Solcitor to write
to her Mortgage Lender.
I hope this assists and sets out the legal position.