NO. It doesn't matter how she sleeps, with or without bra, clothing, etc. Breast cancer is not caused by contact.
No. Breast cancer has nothing to do with what type of bra you wear, how often you wear it, your sleeping habits...
Bras don't cause it. Bra use in of itself is not even remotely associated with breast cancer but breast size i.e. Larger volume is so get your mammograms done regularly especially over age 50.