I don't think that now is the time to worry about her pain meds. She really needs love and support right now. Not people making her feel bad about using something that her Dr gave her to help with pain. Also, Not everyone who uses pain meds is abusing them. Some people really need them. She is using them for the reason they are prescribed. It is like if you judged a diabetic for using insulin. It is her medicine. I agree with the above post that her reaction is totally normal. She needs to greive. If she was over using her meds she might be emotioally numb and show no emotion.
Even if she is abusing her meds, now is not the time to worry about it. Deal with the meds in the future if you still think it is a problem. But you certainly can't base anything on how she is acting right now. Everyone reacts differently to tradgedy. This is not her normal behaivior. Just be there for her as much as you can and help her through this horrible time in her life.
Much love to the whole family. I am sorry you are going through this tragedy. Best wishes.