I wouldn't say I expect it. I try not to expect things from people (except my husband!) I guess my thought it, why not call her?
I've never thought of only saying Happy Mother's Day to your own Mother. My husband was surprised that I was hurt when he didn't do anything for me on my first Mother's Day. He said, "But you're not my mother." Yes, I realize this, but I am the mother of his children!
I do call my sister. I would have called both my SIL's and my MIL, but I saw them so I didn't.
I did not call my girlfriends. I wish I had at least sent them a text, but I think I will a little later and say "Happy belated Mother's Day."
I'm not trying to criticize you, but I wish people would let go of the idea that the person they're calling has to have that specific role in their lives. Saying Happy Mother's Day to the mothers that you are close to is really thoughtful and sweet. If you would call them on their birthday, call them on Mother's Day or Father's Day.