More info on O

So my sister writes;

O +

Hmmm... the plot thickens. We now know...

My Dad MUST be BO +/+ or BO +/-, which regardless is the same immunologically as I am so it doesn't matter which.
My Mom is OO -/-, which is the "universal donor" type and the most dangerous for having kids (to the baby). She must have had a rhogam shot with my sister otherwise I probably would not have been born.

I am BO +/- and sister has to be OO +/-.

Ta da! Now I don't even need to ask my Dad.