Any recommendations for agencies to organise passport application for dual nationality person

[HeadFairy]

DM has dual nationality UK and French, but she hasn't had a French passport since the 50s (I know!). Does anyone know of an agency that could advise and then help her renew her much lapsed French passport?

Why does she need an agency?
uk.ambafrance.org/Passport-21815

Because she doesn't have a lot of her documents. Her birth was registered with the French embassy but she was born during the war so she has no idea if they still have those records. She had a French passport until she was 20 when it was stolen. She didn't replace it as she just used her British passport, so she hasn't got an old passport to send in for renewal. Basically she hasn't got anything to prove she's got French nationality, so thought someone might be able to help her track down those documents. Language isn't an issue, she speaks fluent French and English.

She should start by ringing the French embassy/consulate.