visitor visa extension

[sandy_madison]

My mom is in the US for a 6 month visit and I-94 expires on May 25. She has a 10 yr multiple entry visa and this is her first trip. I am planning to apply for extension in the 1st week of April. If her extension is denied (say, I come to knoe this by May 15), is her 10 yr visa still legal if she leaves before May.25 or does the 10 yr visa get automatically cancelled/revoked once your extension is denied (even if you leave before the date on your I-94)?

Thank you!

[immihelp]

10 year visa is void if extension is denied.