How about just "Happy Birthday!" and leave it at that? It gets the sentiment across but has the added value of being a 180 from what you'd normally do. She can wonder why you were so succinct and mysterious.
ME: 38 BF: 40 T: 10y, no kids, no M (by choice) BD: 7/14/14, BF admits to PA, wants out, lies about new R. 10/1/14: I move out, BF lies about move in with OW 12/4/14: OW confronted, reveals all the lies
