Applying for citizenship but don't have my partners naturalisation reference number

Hi all,
I am applying for naturalisation through my British wife but we can't find her certificate to fill the reference number in the AN form. I know that she can apply for a replacement but it will take 12 weeks and costs £250. does anybody knows what will happen if I don't provide her reference number and tell the home office we can't find it? (she has a valid British passport to prove her citizenship).
Thank you in advance for your help.