No, it is not illegal for a daughter to spend time with her father — and surely you must know that. You’re attempting to spin this story into something it isn’t. It has nothing to do with a daughter spending time with a father.
It has to do with a specific daughter — Ivanka — who is being handed the reigns of her father’s business, which father happens to be the president-elect, and then sitting in on a meeting between her father and a foreign head of state.
And yes, Obama took his wife with him on foreign trips. That’s a standard practice of first-ladies and president’s families. BUT, those spouses (or children) were never in charge of the president’s blind trust at the time, either, and had nothing to gain financially from such trips.
Surely you aren’t so dense you don’t actually understand how what Trump did here is an unconscionable conflict of interest and terribly unethical, and that it has nothing at all to do with the legality of family hanging out together. Your spin is making the world dizzy.