What deeds exist? Did you/mother execute a Trust Deed showing who owns what %? If so, a gift by her to you (and a legal Transfer of title to your sole name) would be required.
The 7-year thing is to do with Inheritance Tax. Subject to some allowances, a gift is free of IHT if donor (ie mother) survives for >7 yrs thereafter. If she dies within the 7 yrs, part of given amount is deemed within her estate for calculating IHT liability. Gift would still be valid, and no IHT anyway if total estate is less than threshold for tax (changes annually).