Mothers name of Jesus

This question is quite problematical in that it assumes the correctness of the false presupposition that there was such a relationship. This is of course entirely false and without foundation, although often repeated.

There can be no name for a non-existent child of a non-existent relationship.

No evidence of any substance can be produced for this since their is none.

it was said that their first child's name was sarah. it means princess.

The Bible does not say anything about Jesus and Mary Magdalene having a child. I don't know your source of information, but if ever they had a child, it will not be a girl. I don't know of any female firstborn; all firstborn (?) of Holy Men in the Bible were male.