Mine is 22 old and not last couple years has less and less leaves in its canopy.

I don't know about Miss Kim in particular but Lilacs are known for their longetivity. As in hundreds of years. My grandmother had one in her yard in Unionville NV in the 1960's that was clearly visible in a photo taken in the 1860's.

It may be that your lilac needs some nutrients and fresh soil dug in around it.

Daisy