Maybe she doesn't want to make things awkward for her. Plus, she spent her whole life looking at her as her aunt. That she'd be her aunt or her mother, it's not gonna change anything now...
And I would imagine Lily didn't say anything either so she wouldn't have to explain herself, or because she didn't want to hurt Chuck...
In either case, it's hard to understand someone's motivations for doing or not doing something. So suppose we'll have to wait and see 'til... whenever
