Speaking as someone turning 50 this year herself, I would strongly suggest avoiding any 'sarcastic' themes such as wakes, funerals etc....
Why not make the theme nostalgic from her 'day'? I would love to have a party with all the music that I loved when I was young (70s & early 80s rock) and maybe have everyone dress like the times - not too hard to do. They had someone playing an acoustic guitar that was all 'unplugged' versions of rock classics - really fun. Also, I was at a party recently where they hired a psychic to do individual readings, she was in a separate room where they hung tie-died sheets and peace signs and smile faces on the walls and had citar music and incense going...really took me back.
One of my friends' husbands recently presented her with a funeral wreath on her 50th birthday, thinking it would be a big laugh. She broke into tears in front of everyone, so you might want to be careful with that.