رضا: As I said, I'd use the words as Marfitalu has. If she is going to be upset, then "must" it is.

There's one thing about this whole deal, when it comes to which word to use. Most people around here could care less as to which is used. These meaning for these uses are somewhat subtle in their differences. I doubt if anyone would even notice in a conversation which one you had used unless you added special emphasis to it while you were talking. Other words can get people worked up. And then there's obscure ones like the word "whom". You got me who uses it, but there really is a proper way as to when to use it. I think the word "whom" will eventually disappear from American English.

One I was a kid, saying "ain't" was considered very bad. Not so much now. It's a right handy contraction.