Because you are not at least 65 years old by the end of the year, you apply the 10% threshold to all of your itemized medical costs (which include costs related to your mother). If she claimed them on her own return, she could apply the 7.5% threshold.
Payments within one tax year of the entire amount due to a participant in a qualified retirement plan. Qualifying lump sums may be directly rolled over tax free, or, in some cases, are eligible for current tax under a favorable averaging method.