I am a US citizen. Is it easier and cheaper to petition my Filipino mother while she''s here in the US visiting or while she is still in the PHilippine

Usually it is easier and cheaper but caution: if she comes here on a visitor visa for the purpose of filing adjustment in the U.S. that is a very big problem misrepresenting her entry. However if she is already here and entered for another purpose she can do this with some restrictions. You should contact an attorney.