The withdrawal will not really help. Immigration is now somewhat aware of her intent to come to the US for a green card, so they believe if she visits she won't leave. You can file again for the B2, but get a attorney to do it this time, you'll have better idea of what evidence you'll need.
She is married to your brother whether or not her name is on the visa petition. However she could notify the national visa center that she does not wish to immigrate, and whether that will affect her application for a tourist visa is impossible to know.
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 issue is her immigrant intent. If she has not done so in her 2 failed visa applications, she should provide a lot of documentary evidence corroborating that she does not plan to immigrate. Such evidence would include proof of a well-paying job in her home country, home ownership in her home country, husband and children and parents living in home country, etc. Withdrawing her name from the I-130 will not help. Call me if you want to discuss for a few minutes. 216-338-2120. [No charge.]
You should always consult with an experienced immigration attorney to make certain that the advice you received is appropriate for your particular immigration case.