Generally, keep her lower in your load order (especially after other custom-voiced follower mods) to ensure her appearance and voice scripts load correctly.
Tired of the same old "I've been looking for you. Got something I'm supposed to deliver—your hands only" from that scrawny vanilla courier? It’s time for a change. Lily - Skyrim Messenger and Follower
Do NOT set her home residence via other follower mods. If you do, she might get stuck there and you won't get your mail!. Generally, keep her lower in your load order
is a fantastic mod that does double duty as both a fully-voiced courier replacer and a recruitable standalone follower. What makes Lilly special? Lily - Skyrim Messenger and Follower
Works great with Extensible Follower Framework (EFF) .