Is it normal for my mother who is maybe a year into her dementia, to just completely make up stories?

Yes, it happens frequently when someone suffers from dementia. My mother claimed that when she had a bowel movement, she “filled the bowl”. That would have been what, about four or five gallons of feces? But, to her, the bowl WAS full.

The most important thing is to not argue or try to convince her she’s talking nonsense. It’s not nonsense to her. Just go along with it. Tell her you’re sorry she wasn’t feeling well and change the subject.

Ditto what Ahmijoy posted with my MIL. Would tell us one thing, then same day tell the 2 other brothers 2 different stories. Was driving us nuts until we figured out she has memory issues and dementia.

Yes. This is dementia. This is not purposeful "making up" stories. To her, in any given moment, everything is quite the truth, and may change seconds later. It is real to her, despite your knowing it is not real. Argument will net you nothing, for to her it is as real as your own reality is to you.

Yup, it’s possible I find it disturbing at times when mom tells stories that are untrue to medical professionals about family and her caregivers. Luckily doctor will try catch my eye when she says strange things. The stories are usually about someone depriving her of something or taking advantage of her.
I try not to correct her, because in her mind these are her truths and she will defend herself with a passion. As you mentioned mom may make an crazy accusation and if you ask about it later she’ll say something different. Unfortunately there’s no reasoning with a broken mind.

Normal? Hmmm. Is there any normal in all this? My mom has never once remembered she has already had her meal, a bath, a walk, or had anyone do anything for her. However, she always remembers what she makes up, word for word, repeated day after day, month after month, year after year. There are enough stories at this point that she no longer has to make up new ones to fill up her brain.

My LO told lots of things that were not accurate. Some were delusions, other false memories, loss of memory, etc. She had no ill intent though. Try to ensure that your family members are aware of how this works.

Mine makes up things about me and tells strangers. Ex. we got two used appliances the other day and before we left mom says, she'll (meaning me) be back she's going to buy a refrigerator. So, I'm like 'what???' Where does that come from? My fridge is fine.
I wonder where they get the ability to free form these stories? It's worrisome for many reasons. But I'm thinking safety issues because there may be non family members without good intentions.

Has a particular type of dementia been diagnosed? One type has more hallucinations I think. Or being sick could be an old memory that just popped into her head?

There's a sort of word salad, mixed up sentences/memories/ideas that some people get. Sometimes triggered by a word. Like if someone said the word *sick* a story/memory may be prompted. So hard to know but worth mentioning to the Doctor to rule out other causes.