Yes, I think that Yvonne Ridley is effective in her opposition to Zionism, because her story by itself is so compelling that it gets people's attention. Ridley converted to anti-Zionism after having been held captive by the Taliban. That is compelling enough that she is effective in sharing her story with others.
I find Yvonne Ridley to be one of the most interesting journalists and activists in the world, in just about the worst way possible. Anyone who gets kidnapped by a religious regime, converts to their faith, and then speaks out against another faith is pretty much a fool in my book.
I believe Yvonne Ridley has been effective in her opposition to Zionism. I believe Ridley has found groups and others that support her views and she has shared her views with many other people. As far as spreading those beliefs and voicing her opinion I feel like she's done very well.
In general, opposing something only promotes it further. Yvonne Ridley might have some good points to make, and there is some truth to it. However, she just opposes Zionism and does not really instead advocate an alternative. A war to end all wars is still a war, and the supposed war on drugs only increased drug prices and drug lord wealth. In the same vein, Ridley is giving Zionism attention instead of really hurting it.
I do not think that Yvonne Ridley is effective at all with her opposition. I do not think that the way she is going about and protesting the issue of Zionism is going to be beneficial to the people who agree with her. I also think that it will not change anything.