Yes, it's open to everyone but generally speaking, and speaking only from my own experience as a leader, is that the girls and families who are in Girl Guides and Girl Scouts tend to be of similar mindsets - this does not in any way reflect socioeconomic situations. Also, once the kids hit a certain age, such as 13 and up, it tends to not be 'cool' anymore and there is a definite split in mindsets at that stage. It is self selecting, not imposed by the organizations. I did not mean to imply otherwise at all and I'm sorry if it came across as such.
I have been a leader in Girl Guides in Canada and the UK and in Girl Scouts in the US - I've seen the programme promote the self esteem of so many girls. It's a fabulous organization.
I was a brownie then a girl guide until I was 13, then I discovered boys and drinking.... so I would agree with MrsPink here that it's very self selecting, when I was at school girls of 13 ran the gamut from very innocent to much more mature and things like girl guides where highly correlated to which end of the spectrum you were on.
In the same way a lot of girls did ballet and pony riding before this age, but those activities either got serious (more equestrian and professional dancing) or they became uncool and stopped.
I think girl guides is a wonderful program and I really enjoyed it, but felt a lot of pressure from my friends to do more mature things so it's one of those things I left behind, like my clarinet
I would second the idea of the Duke of Edinburgh award, that;s a great way of meeting people and you get to do lots of interesting things.
Is it worth actually asking her what she wants to do, you may be surprised, like she may have a secret passion for surfing, rock climbing, horse riding, playing guitar, skateboarding, cheese making or whatever, and it would be much better if she could pick an activity she's interested in.