Can a husband forbid his wife from taking care of her parents financially?

No. Her own personal income is hers, and she has a ethical, moral responsibility to her parents.

This idea that only men have a financial responsibility to care for their mother and father is not true. If a woman has her own money, she also has a responsibility to care for her mother and father when they cannot care for themselves and her husband cannot preclude her from doing so.

Unless, of course that was harming the family in some way.

There are times where, a woman doesn't have her own personal income or she's wasteful of her personal income and so she dips into her husband's income to care for her family.

Get your own personal income in order first, and then care for your family.

That way you're not putting stress on your relationship and it happens the opposites as well. I've seen a lot of men who will be extremely wasteful with what's at home and then expect their wives to also take care their parents, which is not acceptable.