So, I have noticed the sims 4 game doesn't automatically change her last name to her husbands last name.. I'm all for women having the choice to keep their name or take his last name in marriage but, I would like the game to ask if the name is to be changed. so, the household has the same last name..My question is are there a way to change her name without having to do the cas.fulleditmode cheat?

The cheat is no longer required, you should be able to change a sim's name anytime.

Other than that, if you are using the Mcccommand center mod, it lets you set your preferences for name change after marriage and also an option that synchronizes household names. I don't know on top of my head which module of the mod exactly you'll need for that (Mc Population, I think).