Thank you for your question
My name is ***** ***** I shall do my best to help you
You are correct - your mother would be committing a criminal offence if she did this.
Indeed even agreeing to the Deed of Variation would be an offence on her part in terms of amounting to "deprivation of assets"
Please ask if you need further details
Yes it would indeed be aiding an abetting - although a prosecution for you is unlikely - for her it would be certain