Because you have a cousin named Lila I wouldn't consider Lilac for a first name. I feel like Lilac, which is one of my favorite girl's names as well, would be mistaken for Lila quite a bit in general. Not to mention if she has the same nickname as your cousin's name!
I can't think of any nicknames for Lilac other than Lila or Lil, which is not very intuitive.
It bums me out! I could always use it as a mn
Maybe Lyle (though it's really masculine for Lilac). How often do you see your cousin? That could make a difference in whether its too close. There are quite a few Sams (male and female) on one side of my family and that doesn't seem to stop anyone from using it. However, that side of the family is quite scattered about and only gets together on holidays.
For me it would depend on how close you were with your cousin. Personally it wouldn't deter me from using the name but if it would cause family issues than I would avoid it.
I agree that if you are not around your cousin a lot, then it would be fine.
I love Lilac as a name, so sweet! But agree with others if this is a cousin your baby will grow up around, then it might be too similar! But if it's a cousin you don't see a whole lot then I don';t see the big deal. But on the other side, your cousin might be honoured that you sort of named your daughter after her. Even if not entirely true, might make some people feel good! So could go either way. No matter what, beautiful name! It just so soft and sweet..also love that it has personal meaning for you.
I say Lie-lack and am in NYC area. I think it's such a great name and even though it sounds similar to Lila it is so distinct. Maybe Lola? I wouldn't even shorten it as it's so nice. You could probably use Lee. Or do a double name and make a nickname out of those. I put some examples below cause I don't know if I'm explaining it very well!
Lilac Grace = Lacey / Lace
Lilac Elaine = Lane / Laney
Lilac Olivia = Lolly
Lilac Rachel = Lira / Lyric
Lilac Noelle = Lina / Lena