I want my mother-in-law to plan events better
What does your mother-in-law do that bothers you?
She is just bad at planning
It is ok to ask or try and help out planning events with other people. It might just help if you take charge of the plans for her to get things done right.
I really hate these family get togethers especially when they're planned bad.
There's nothing wrong in giving suggestions and give constructive criticism to your mother-in-law if she's not able to handle events properly. As I said you should help her in family get togethers.