I don't know if I know, how to label it?

With dementia, mostly anything is possible!

Your profile says that your wife has dementia, which at her young age must be early onset Alzheimer's, so I can only guess that it's not normal but part of her dementia, unless she was like this prior to her diagnosis.
The fact that she can still navigate online websites and write letters, tells me that she is very early in her diagnosis, so just take whatever precautions you need to like limiting her credit limit on her credit cards, and the like.
OCD is one of many of symptoms of the disease, so not surprising that she's fixating on things.
If she's already driving you crazy this early in her diagnosis with her actions, you best be getting your ducks in a row as you'll never be able to handle it when her Alzheimer's really kicks in.
Plus early onset Alzheimer's can last up to 20+ years, so you're in for a very long and difficult journey.
I wish you both well.

I agree with those who suggested putting tight controls and protections on her financial assets and social media. If she's uses FaceBook she is a prime target for scammers. There is currently a new post from someone who's Mom is being financially ruined by Nigerian "celebrity" scammers.

- consider moving as much cash as possible out of her (or joint) checking and into savings, leaving only enough to cover bills and expenses. Give her pre-paid Visa cards with low amounts on it. Don't tell her why you're doing it, just do it. Then give her a "therapeutic fib" that she will accept in order to keep her calm over it.

- consider a credit alert system (like LifeLock) so that you'll know if someone is using her identity fraudulently

- on any bank account you share, make sure you've given them your PoA paperwork and tell them to monitor your account for unusual activity (a small town bank may be more able/open to do this)

- make sure you hide checkbooks and blanks; consider changing the passwords to online banking and assets so that only you know them; etc.

- any and all of her social media access. Ugh... parental controls? On every device.

- consider giving her a tablet with games but no internet access; consider getting her a phone with no internet.

It only takes 1 opportunity for scammers to get to her and do significant damage. That money will never be recovered and they will never stop coming at her for more. The other poster's Mom was convinced by the scammers to get a burner phone and contacts them on that. They convinced her that her family was the problem. Paranoia is part of the disease, too. She will be angry but at least you won't be broke.

I wish you success in getting things under control.

You're kind of describing my DH who, when he finds something that piques his interest, will do a deep dive on it. Literally, hour upon hour researching reading about..... whatever. He has terrible ADD, won't medicate for it, so his amazing focus on things that are different or new to him is just, well, him.

Actually, I use it to my advantage. I ask him a ? I know he doesn't have the answer to and then let him spiral into finding out everything he can about it.

Currently, it's bird nesting boxes and how to make them and set them up to attract specific birds to nest in them.

He's made and gifted about 6 of them and is having a great time with this. And he's out of my hair, wandering around asking if there's anything to eat.

My kids joke (but it's not funny) that their dad is pre-demented. I probably won't notice if he starts sliding into dementia, he's already kooky.

I am so sorry that you are going through this difficult situation with your wife.

You cannot change the way your wife views the world. You can control what you are willing to tolerate.

You could speak with her doctor about your concerns to see if an adjustment in meds would help.

I would cancel her credit cards. You can open up a separate account and give her a debit card with only a limited amount of money to spend. I don’t see a reason why she needs to have any credit cards.

Wishing you peace as you continue on your caregiving journey.

Your wife suffers from Alzheimer's/dementia so many of her behaviors will not be normal, in reality. OCD type behaviors of any kind are common with any of the dementias, so becoming fixated with online shopping or research is not unusual. You may have to put spending limits on her credit card if she also becomes obsessed with ordering things online.

I think the important thing is here, is this NORMAL for YOUR WIFE
Or is this a big change?
If this is a big change, what other changes are you seeing.
Can you play a game with her in which she attempts to spell words backwards. Forum, for instance? Can you divert her with a card game? Is she able to discuss issues with you she could always discuss?
Is the shopping online something new (and by the way, cancelling he credit cards will stop that real quick; just get rid of the card she has and ask company to issue you a new number if you feel she is spending beyond your means for things she doesn't need or is falling into Hoarding. Of interest is that Hoarders do a huge amount of online shopping.

Only YOU know your wife and know what things you are observing.
If these are changes you would be the one best to judge this and to discuss with her, and attend a meeting with the doc with her.
Early stages of dementia manifest in interesting and individual ways.
I surely do wish you the best and hope that this is a matter of boredom, easily cured with doing board games, card games, puzzles or walks together.