Iris snooped in and took Elder Tilrith's place as the one who would view Rex's past.
Surely, she was annoyed by that.
Her scowl showed that clearly for anyone to see but the warning she gave before Iris leaped into the trench was a genuine warning. Iris could tell that Elder Tilrith was really warning her, that peering into Rex's past was not going to be easy.
Regardless of wanting to know Rex's weakness, Elder Tilrith was fitted for this role.
She and Rex were in the same position so she could better endure Rex's past.
Older usually means wiser and stronger.
Going with that, those who lived longer will always be wiser and stronger.
But in reality, that wasn't always the case.
Time alone would not be able to make someone stronger or wiser, experience was the main driver, the only reason that saying exists was because living longer meant having a lot more opportunity to obtain experiences.
