Is my cousin's mom still my aunt?

They will both be your Aunt.

Depends on your family...some families end family titles with divorce and some don't. As a sign of respect or friendship you could still call Lynn your aunt. You could also ask her or uncle Trevor what she would prefer to be called. Most people wouldn't question whether aunt Lynn and uncle Trevor are still married unless they know about the divorce and even then, to make it easier for all they would still refer to aunt Lynn as aunt Lynn. The other option is Aunt Lynn--uncle Trevor's first wife or Aunt Lynn my cousin Suzy's mother.

since Lynn and Trevor are separeted legally by law, i don't think you can still consider her as your aunt by law

If you run into her you should say with a big smile Auntie ! if smiles back you'll know.