You know how strong rosemary can be -- so as long as you don't use too much in either dish, it should be all right. If it were my menu, I'd use another herb on the beef. But as Mark said, it's
her party.
That said: are you going to do a "tryout" of the menu before the actual dinner? If so, then maybe she'll decide that the repetition is too much, and she will want to change something. It's always better if the client thinks it's her own idea.