Thanks a lot for the information.
Two more questions:
1. how to apply? where can I find the detailed form? is it online?
>> File form I-539, which can be found and downloaded on USCIS website, and which can be filed online, besides mailing.
2. my mom want to stay more time with family. Can we say she need more time to "stay with family and need more time to travel here in the U.S."?
>> That's reasonable. however the more detailed and personalized plan you can draft, the better.
Thanks a agin.
>> You're welcome.