Am I obligated to marry a girl with whom I committed zina unwillingly, knowing that my parents desire her because of her good treatment of them, or should I search for a chaste and religious girl who would help me in this life and the hereafter?

You must initiate repentance to Allah Almighty from fornication by abandoning the sin, regretting it, and resolving not to return to it.

If your repentance and her repentance are sincere, then there is no blame upon you in marrying her, for repentance erases what came before it. If you do not repent or if you are unwilling to marry her, then there is no blame upon you in marrying someone else.

There is no disobedience to your parents in this, as neither parent has the right to compel a child to marry someone they do not desire.

However, you must be dutiful to your parents and treat them with excellence, for their right is great, and being dutiful to them is among the most obligatory duties.