Thank you for your question
My name is Clare
I shall do my best to help you but I need some further information first
Has the Charge Deed been drafted - what does it say about payment?
My apologies for the delay
It is unlikely that the Mortgage Company will accept this as they generally need you to express it as a gift
You would then need to have the Legal Charge drawn up signed and Registered after the completion of the purchase, and a separate agreement between you and your niece detailing this.
The terms that you have set out will allow you to force a sale should the need arise.
However you will need to check that the Legal Charge deed is correctly drawn up.
I hope that this is of assistance - please ask if you need further details