If your mother is a Qualifying Relative, then yes you can claim the medical expenses you paid on her behalf.
The IRS defines a Qualifying Relative as someone:
"Who is your:
Son, daughter, stepchild, or foster child, or a descendant of any of them (for example, your grandchild),
Brother, sister, half brother, half sister, or a son or daughter of any of them,
Father, mother, or an ancestor or sibling of either of them (for example, your grandmother, grandfather, aunt, or uncle),
Stepbrother, stepsister, stepfather, stepmother, son-in-law, daughter-in-law, father-in-law, mother-in-law, brother-in-law, or sister-in-law, or
Any other person (other than your spouse) who lived with you all year as a member of your household if your relationship didn't violate local law,
Who wasn't a qualifying child of any taxpayer for 2015, and
For whom you provided over half of the support in 2015."
(From: IRS
Publication 502)
