My mother was unable to make up her missed fast days before she passed away and she did not pay kaffara for those days. Is she blameworthy? 

Scholars concur that a person is not to pay kaffara [expiation] or make up the fast on behalf of a deceased who broke his fast due to an excuse that continued until his death. This is because the deceased did not neglect to fast and is therefore not blameworthy. Like pilgrimage that is an obligatory act of worship that is waived for those who are unable to perform it, fasting in this case, is likewise an obligatory devotional act that the deceased was unable to fulfill until her death and therefore it is waived for her.
And God Almighty knows best.