Is one sinful if one resents their father and avoids dealing with him, especially if the father dislikes his daughter's religiosity, tries to exploit her financially, and threatens her with problems with her in-laws?

The father's right is great, and he must be obeyed unless he commands disobedience or harm. You must treat him with kindness through good words and gifts. As for your inner feelings towards him, you are not held accountable for them. It is permissible to reduce visits as long as it is not considered abandonment. If the marriage took place without the father's consent, then if the contract was overseen by the Muslim ruler or his deputy, or by a more distant guardian because the father unjustly withheld his consent, the marriage is valid. However, if the contract was concluded without any guardian at all, it is invalid and must be renewed.