Uh-oh. I went to my best girlfriend’s funeral at an Episcopal church. Was that wrong? (I was, by the way, very aware during the entire thing of the hollowness of the service.)
No way is attending a funeral wrong.
One of the corporal works of mercy is burying the dead. We fulfill that by attending funerals.
Talk with the priest about it. It would be different, in my opinion, if you were checking out that church and leaving the Catholic Church for another.
But you were honoring your friend by attending her funeral. I don’t think that is wrong at all. But then I’m not your confessor.