I would just take her to the doctor. Sounds like she is pretty normal but may need a b-12 shot or something, hopefully!
Hum, hard to say could be anything, not sure it's anything to worry about, I say have her checked out
No, she doesn't repeat things ever. She only mixes up words. It isn't severe at all - it happens maybe once a day or once every other day - but a worrier like me has noticed it.
She doesn't confuse night with day, just the words. She always gets frustrated and says "do what I mean, not what I say"
The first thing to do is take her to the doctor and get a regular exam. Gently bring up your concerns so the doc can run tests on thyroid, vitamins and things to rule out simple things that can cause issues.
Some being absent minded is pretty normal. So you have to understand what is normal, and what is dementia. Dementia starts out pretty mildly, but progresses to encompass the entire body. If she is confusing day with night as in not sleeping at night and sleeping during the day, then that is known as sundowning. That is a symptom, but I would guess the rest is normal.