Per IRS Publication 501 your mother is would be considered permanently and totally disabled if both of the following apply:
- She can't engage in any substantial gainful activity because of a physical or mental condition.
- A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death
You will need to obtain a letter from the doctor stating that your mother is totally disabled and maintain it for your records. You do not need to submit it to the IRS unless requested.