Looking back at the previous chapters, even their first introduction, and this latest one, she seems more like the caring oldest sister troupe. The sibling that puts aside their own wants and desires to help the younger sibling who has it worse in some way. In that same way, Lily is the middle sister who notices this is going on, so when she was younger she tried taking it out on Ashley but now she's trying to support Iris however she can. The fact that Lily took that veil material aside, it may be she's hiding it for her own personal use (in which case I'm completely wrong) but it seems more like she recognized what Ashley wanted to be, saw the veil material would help Ashley and despite probably wanting it for herself, put it aside to hold for Ashley. And lovely Lily acted so well gaining their mother's attention back without causing any sort of fight or blaming Ashley, ah she's maturing!