In 2013, the AGI floor for someone under age 65 is 10% of AGI. The 7.5% floor applies to those 65 or older. Since it is you, and not your mom, who is taking the deduction, you must use the 10%-of-AGI floor.
A husband and wife who are required to live apart from each other by the terms of a decree of separate maintenance. Payments under the decree are deductible by the payor and taxable to the payee as alimony.