I was told before, if a man has has orgasm during foreplay with his wife and no liquid comes out, he does not need to do ghusl.

Does this also apply to the wife? If she has an orgasm during foreplay but no new liquid comes out or she is not sure if any has come out, will she still need to do ghusl?

What if it’s just the same moisture that was there from arousal and she is not sure if any "ejaculation" has taken place during orgasm? This is confusing for my wife because the area is already a little wet and nothing really changes when orgasm happens.

It differs for women.
If big amount of fluids was discharged from her, even before orgasm, then she needs to do ghusl, while if the amount of fluids was small, just around the area, like lubricant, then she doesn’t have to do ghusl.