I know you have the opinion that she 'stupidly' put her partners name on the birth certificate, but infact she would not have been legally able to do this, her partner must have attended the register office himself to have his name added to the registration. Your grandchild will always know who her natural father is, and she will not have to take her birth certificate to the vicar when she wants to get married and show that she did not have a father included. Her birth registration name is taken as the one of the father, however, you can legally use any surname on your birth certificate, even though she is registered as his surname, she can use her mothers surname if she chooses, or if her mother chooses