If those goals are at all ambitious (like, say, being a world leader for a really long time), yes. Of course.
Now, it appears we're talking about two separate things, or at least we've divided the argument in to two separate things. Yes, they are successful at achieving what they want, but within the context of the original post, success should be judged on the quality of not only achieving what they wanted, but doing it well enough to be judged as such in general, by the public. The OP seems to be suggesting that women are chosen because we know they are quality, are capable, as opposed to being chosen "for the sake of it" but I am suggesting that in the example they chose it proves it not always to be the case, and there are other factors to take in to account as to why a person may have been able to achieve their "success".
This simply doesn't follow. The only way someone can be successful/capable no matter what they actually achieve is if they never set any notable goals for themselves. That obviously doesn't apply here.
The inverse, however, is absolutely true: if you deny someone's capability because they had different beliefs than yours, then virtually everyone can be said not to be capable to an extent.
I'm not sure what the argument is here, other than "but I really really really don't like her, so I don't want her used as a positive example of anything."
What I'm arguing is that ultimately whether a person is a success, or once again going back to the OP's original point, a capable person, then there has to be evidence to back that up beyond someone simply being a leader, or being elected. As much as you think it's fair to say she was a success in the fact she became leader, and was re-elected twice, I think it's fair to say that now the majority of people will agree with me that her tenure was one of the worst in the 20th century, and the consequences of what she implemented destroyed many lives, and still do. Whenever you're judging success/capability then there will always be split opinions, so I don't see how your criteria for success is any more fair/unfair than mine.
And yes, your right in saying that if you judge certain ways different to others than you can make an argument that everyone is not capable. But generally, when it comes to judging people, there always tends to be expectations and places of agreement where people can be judged against other people.