How do I get permission to do temple work for a relative who has no close living relatives. She died at 15 in 1945, survived by parents now dead and one brother now deceased.
An article in the Help Center will give you step-by-step instructions for seeking permission to do the temple work of your relative.
These sentences are especially important for your situation: " If no close living relatives exist to grant permission, you can still request permission to do the ordinances. Please provide evidence that no living close relatives exist."
"If no close relatives are alive, make sure that Family Tree contains their death information. Attach sources as evidence."
Here is a link to that article.