Retail business valuation expert

I want to go into business with my friend who runs and owns a small boutique womens and lifestyle shop in Marlborough with online presence via own website & trouva. She is currently breakeven with net liabilities so all standard models value her business at £0. However business owner has a figure in head that we’re struggling to agree on so need someone to value the intangibles of the business in her brand etc.
also need to understand how to close deal:
Ie. Sale of 35% shareholding or capital injection via share issuance to dilute current director to 65% abs the impact this has on valuation.
Thanks.