"She'd be great at this job if she didn't need wheelbarrows full of marijuana to function" - Delilah
Delilah briefly mentions her sister to Henry while he is on his way to collect supplies from a recently re-filled food cache to restock his tower.

She comes to mind due to Delilah theorizing that there may be prunes inside the box, which in turn leads to an anecdote about how She (Delilah's Sister) eats exactly six prunes a day, with precision.

According to Delilah, her sister apparently also uses a lot of marijuana.

Delilah's sister is never seen or heard from, all we know come's from Delilah's anecdote.