I can understand your feelings, but as her closest relations, it was up to her children to decide things really. Perhaps she had told them herself she didn’t want a lot of fuss, and preferred a quiet send off?
It appears they took up some of your suggestions, and allowed your family to take part. Regarding the reception, maybe it wasn’t just the cost, they genuinely didn’t want one. As for obituaries in the local paper, yes, that was very commonplace in our town years ago, but now it’s quite expensive to place one in, plus the local rag isn’t ‘what it was’, and not many people buy it nowadays (me for one). You see more local deaths on the Facebook page.
It’s sad you are now estranged. Is that what your sister would have wanted? Life’s too short for bad feelings.