I'm so sorry you've suffered such terrible, traumatic losses. To lose one sibling is tragic; to lose two, unimaginable.
I'd try to view her response in the context of your general relationship with her.
My SiL behaved not dissimilarly when my mother died very suddenly and at a young age. I received no condolences from any member of DH's family at all. SiL invited herself to stay two days after the funeral then phoned MiL right in front of me, whining about what on earth she would do without a mother to talk to. I had just buried mine.
Unfortunately this was a case of once I'd seen her real character I couldn't unsee it, and her behaviour in the two decades since has done the reverse of dispelling that impression. Even DH is now out of contact with her.
As if a bereavement isn't painful enough, sometimes it shows us who is really there for us and who isn't.
Your MiL's behaviour isn't on the scale of my in-laws, and if the relationship is otherwise warm and loving I'd let it pass. In my case, it at least did me the favour of showing me what they really thought of me. I hope yours will later come through for you and your hurt will prove to be unfounded. All I would suggest is that you don't act hastily: grief isn't necessarily conducive to clear thinking.
I wish you healing and peace 