If you can show an insurable interest in your grandmother, and she is insurable, "Yes" you can insure her.
An insurable interest would be a family connection and something like the purchase of a life insurance policy and payment of a life insurance policy for final expenses. Usually, insurable interest does exist between family members, siblings, spouses, parents and their children, etc.
If the face amount of the life insurance policy was too high, you may be asked to explain the need for that much life insurance and the offer might change.
If you can't show a reasonable relationship between the face amount of life insurance coverage you want to buy and the need, you may not get what you want.
When purchasing the life insurance policy for your grandmother, you may need her to answer a few health questions, and she may or may not need to sign the application for life insurance coverage.
Learn more about how to buy life insurance for a grandparent or parent.