Originally Posted by
alanh
There is, unfortunately, effectively no "transit" in the United States any more. If you land in the US, you're admitted to the US (or sent home), even if it's just an hour or two.
FWIW, I'm pretty sure the exclusion of adjoining countries from resetting the clock is exactly intended to prevent the "day trip to Tijuana" method of getting around the six month limit.
Exactly. The OP's mother may find herself in the same situation if she tried a border jaunt to reset the visa clock. FWIW, this is what the U.S. embassy in Australia has to say (at least with regard to VWP):
Q. I have entered the U.S. on the VWP but now find I need to stay longer than the 90 days. Can I transfer to another type of visa without leaving the U.S.?
A. No, you cannot transfer from the VWP to any other type of visa, and you cannot extend the VWP 90 day admission period. You must leave the U.S., Canada, Mexico and adjacent islands within the VWP 90 day admission period, and either apply for a visa relevant to your new situation, or re-enter on the VWP if your next stay will be less than 90 days and you still meet the other requirements. Re-entering on the VWP is however at the discretion of immigration officials at the port of entry, who can deny admission.
Q. If I travel to Canada or Mexico, can I re-enter the U.S on the VWP, and if so does the 90 days then start again?
A. VWP travelers who have been admitted to the U.S. under the Visa Waiver Program and who make a short trip to Canada, Mexico or an adjacent island generally can be readmitted to the U.S. under the VWP for the original admission period. They do not, however, get a new 90 day admission period.
I imagine the same would apply to visa holders.
OP should really have his mother apply to extend her stay as outlined here:
http://www.uscis.gov/portal/site/usc...0045f3d6a1RCRD