For me it's always been Willow Johnson. She's in a lot of animes like Ranma 1/2 (Kasumi Tendo) and Inuyasha (Kikyo). Both voices fit Lili, though I've always preferred Kasumi's because she says a lot of things that Lili does like 'oh my' and 'goodness'.
http://www.behindthevoiceactors.com/Willow-Johnson/
You can listen to the voice clip here
http://www.behindthevoiceactors.com/Willow-Johnson/
You can listen to the voice clip here