As a marriage is not valid without the consent of a Wali (guardian), will the marriage be valid if she has converted and that her conversion to Islam is against the consent of the parents?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If a woman is a Muslim, her non-Muslim father has no guardianship over her.  So, her guardianship moves to her closest male relatives [provided they are Muslims], and then to the general Muslims.

If she has no Muslim male relative, then the Muslim judge - if any -marries her off.  Otherwise, it would be  the Muslim community who marries her off.  So, an Islamic Association or an Islamic Center marries her off.

Allaah Knows best.