A married couple in a common property state doesn’t have personal assets.

I think it's more complicated then that. For example, me and my wife bought a car together, but it's only in my name. Since we're married, it doesn't matter that it be only in my name, we both own it 100/100 based on our marriage contract. So we don't even bother putting everything in each other's name.

I suspect Amazon was a similar afair. They both quit their job and moved city to start and work on Amazon. When the company began, she was working on it with Bezos, both together.

It's possible that they then decided similarly not to bother with adding her name to the company officially, since as they were married that doesn't really matter. In fact, IANAL, but I'd suspect it might be complicated to do so, since by your marriage you already have a contract with one another, and as a contractual business partner you'd have another contract, and I wouldn't be surprised if that gets messy as both contract can easily conflict and the marriage contract has special status.

So I think it's fair to consider her a co-founder, in that she acted as one, took all the same risks, quit her job, moved city, worked on starting the company, put her financials at risk and invested her own money into it, etc. Even though she's not really a co-founder as registered in the company itself.

Well, from the other side Jeff got the rest for being her spouse. They were married before Amazon was founded, so they were involved in that as a couple. And she also left job and moved for founding Amazon.