Hi, I’m sorry that’s happening, glad you are writing in.
Early-onset or “younger onset” does tend to progress faster than other dementias. My advice is to NOT try to get her to see your point of view. Reminding her that something is wrong with her brain is pretty counterintuitive: because something is wrong with her brain, she cannot recognize that something is wrong and be able to fix it. Instead, work around her impairments and set her up for success. I have a post on here called “dementia care is like tee ball.” We really want to do the background work so that she can feel successful. For example, instead of putting all the groceries on the table and saying, “Please put these away,” you should put all the cold items in one corner and say, “Can you help me put these items in the freezer?” You’re breaking it down to make it easier and when she feels successful, she will feel happier. She’s probably snapping at people because she’s frustrated. She knows, deep down, that she’s lost some of her cognitive reserve. We don’t want her to be unhappy about it more than she is.