I think this is a very difficult question. If I have the details right, your friend is not working, so she basically lives of his income. If they keep a joint bank account it can be difficult to say, I know all the money you earn is ours but now that I had some money come in I am going to make it just mine.
Inheritance usually in divorce court is separate money, not counted as a gain durng marriage that would be divided, unless you comingle the funds, then you start giving up your rights to the money solely and it does essentially become common property to be put into the mathematical financial equation of divorce. The laws do vary by state.
If I inherited 50% or less of what my husband makes in a year (I am not working now) I would put the money in a joint account. If it was more I would want to keep it seperate, but it would be a very difficult thing to do. After 20 years of always having our money together, and the last ten with him being the much bigger breadwinner, if I were in his place I think I would be a little annoyed if all of a sudden some money is separate.
I guess part of the decision is how important is it for that money to go to other family members on your side if you die. It is not just a divorce consideration, but a right of survivorship consideration.
When one of my girlfriends got divorced she was super pissed he left with more money because the courts did not count an inheritance he received. She divorced him partly because he only worked part time, had no real drive to make any money, and other reasons. In the divorce they wound up 50/50 custody of their child so she pays her ex child support, and he walked away with about $80k and she with $20k in savings. His inheritance had been around $60k. She thought it was competely unfair. I don’t, but she did, and I do understand why it frustrates her.