Extend USA B2 Tourist Visa (for My Mother) stay under COVID19 + Flight ban situation

Several months
It's up to you
She can stay until the I-94 expiration date. (It's also highly unlikely to be decided in 2 months.)
She is "out of status" when the I-94 expires, but "out of status" doesn't matter. If her Extension of Status is denied after her I-94 expires, she starts accruing "unlawful presence" immediately starting on the denial date. The visa gets voided. There is no ban if she leaves before accruing 180 days of unlawful presence. They will issue a Notice to Appear for removal proceedings if she hasn't left 33 days after the denial.
Again, she will be "out of status" when the I-94 expires, but "out of status" doesn't matter. She will not have accrued any "unlawful presence", and her visa is not voided.

user102008 20164

Source: stackoverflow.com