M.G.
Usually (at least in my experience) one person takes the lead on things like this. Usually it the person who has been most responsible till then. And sometimes they find it easier to go ahead and make decisions, keeping in mind the deceased's wishes, on their own. Without opening it up to debate to the whole family, or others. Maybe they have good reason for this - maybe so and so has ideas that don't generally go along with the others, etc.
Your mom is likely grieving very much and just wants decisions made. I know when my father passed, we weren't included in anything. My mom, along with her sister for support, just said yes/no/yes/no/that one - to get through it.
I think it is lovely that you have come up with a slideshow. I think it's great you are concerned for the whole family and how they are dealing. She is likely just going through the motions, and may not be thinking of everyone else at this time. Honestly, I think her reviewing the slideshow was not that big a deal. Some people don't like surprises at services - even good ones.
I find these times in life are just people coping. Not always at their best. Everyone is kind of at their worst. And that's ok. That's to be expected. If they're not being generous - that's ok. If they are not thinking of how others feel - that's ok. They are doing the best they can under the circumstances.
It's not your responsibility to make sure everyone is ok. Sometimes people take on that role - but no one is asking you to. If others have a problem with how your mom is handling things - then it's up to them to say something. Keep out of it.
But I'd cut your mom some slack. To her a slideshow may not be a big deal. She just lost her mom. Know that it is appreciated and will be a wonderful way to remember her by. And just move on. I'm sorry for your loss - I get the whole thing can be emotional. I wouldn't make a bigger deal of this than needs be.