The trouble is that the H4 is her petition, not yours. You can notify them that you don't want to sponsor her and they might notify CBP not to admit her. No harm trying.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
The H4 visa was granted to the dependent spouse to enable her to join the principal spouse in the U.S. This is not a traditional petitioner/beneficiary situation where withdrawal/revocation is possible. However, you do not lose anything in contacting the U.S. Consulate which issued the visa about your preference, and it is theoretically possible for the Consulate to rescind her H4 visa.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter, nor should it be viewed as establishing an attorney client relationship of any kind.