As has been mentioned, it's illegal not to have a passport and you can be fined very heavily for this.  It may be that the owner has had her for a long time, perhaps before passports were brought in, and never bothered to get one but I would make very sure that this is the case.  If she has no passport then other things will also have been neglected e.g. vaccinations, the vet has to see and sign the passport each time a vaccine is given and would most certainly have made the owner get one for her.

you can but i would ask about her back ground, my fisrt thing would be is she stolen, unlucky but you never know. ask y she hasnt got a passport?