Welcome to the site. I will be helping you today.
IRS is generally limited to 15% garnishment for income taxes
from Social Security benefits (http://www.irs.gov/Individuals/Social-Security-Benefits-Eligible-for-the-Federal-Payment-Levy-Program) is a link to IRS describing the 15% cap they are limited to taking).
In order to stop the levies, and potentially get funds returned to you, I can suggest hiring a tax
professional to assist. In the event you want to try and remedy this yourself, I can suggest a couple of possible options:
1. File Form 911 with the IRS Taxpayer Advocate Office (http://www.irs.gov/pub/irs-pdf/f911.pdf is the link). Ask for a hold on the levy and refund of any collections over 15% until the case is reviewed.
2. Review your options with a tax professional who does tax advocacy. There may be other settlement options available, depending on how old the taxes are, what type and your mother's means.
Thanks for asking at Just Answer/Pearl.