Possible, I guess, but tbh, if she was into smoking pot she could do that in any major european city. The Netherlands did recently enact a law against 'pot tourism' - they're a little tired of the reputation, I think, so they've made a law that only residents can legally smoke. However, it's apparently not really being enforced, so probably everything's pretty much stayed the same.
As to why go there - without sounding like the Dutch Tourism Board, Amsterdam is an amazing city! It's beautiful, for starters - with some gorgeous museums - including Anne Franks house, a Van Gogh museum... the Dutch are incredibly friendly, it's a great town for tourists because it's small and everyone speaks english. It's a very safe place, too - out of the countries you mentioned I would feel safest in Amsterdam out of major cities in any of those. I personally think it's a shame it has the rep of girls and weed, because that's such a tiny part of it. But it's definitely a place a lot of tourists go, and would recommend - I'd say it's probably in the top 10, if not top 5, stops on the european tourism trail - and for someone who wants to speak English, it's there or London really.