Hmmm... that's a tough one actually. I know my Bday is coming up in Dec and I have no expectations of my H doing anything. IF he does, I will feel like it is only out of guilt. So I'd rather spend it with my S or friends or even by myself.
I would say that you should at least maybe if you can, leave her a birthday card somewhere where she can find it and read it by herself with no pressure of you expecting any thanks. Then maybe later send an email saying 'hope your birthday day is going well' or something to that effect. I don't know if this is right either, but it seems to remove any pressure from her to be happy about you doing this or you expecting anything from her.
Just my 2 cents.
Me:49 H:47 S: 16 T:27 M:25 My EA: 2001 His PA: 10/2007, 6/2013 Separated, but H still in house
Find your Shambala: a place of peace and happiness.