Unfortunately, in the grand scheme of 'dementia' Alzheimers is just another word for the dreaded disease. It really doesn't matter 'which' dementia she's got, the fact is it's dementia. Finding out the specific one can't really be done until autopsy (and nobody is usally in a hurry for that).
Paranoia is a HUGE part of early dementia signs. The person afflicted knows things are going wrong, and can't possibly believe it's THEM, so it must be everybody else. Hence, hiding, hoarding, cunning behaviours and other 'weird stuff'. Hiding is not unusual in my experience, they feel safer and more secure. Some tricks are to not make a fuss when she is hiding, and when found just treat her as 'normal' as possible. The more fuss, the more she'll think something is wrong or up, and that will entice her into more hiding to get away from the fuss. Keep it calm, keep it even. Remove loud noises (music, lots of people etc) remove mirrors (other people to hide from) .. minimise things that can and will scare her.
Look OUTSIDE the box is a rule of thumb .. what may appear normal to you can be totally warped to your loved one.
There are no hard and fast rules with this disease, and I do encourage you to read the 7 stages sticky at the top of this board.