I assume you mean, 'the highest level of education achieved by/reached by/held by women? If so I actually prefer the first phrase. So, yes, 'level of education of women' is correct. But the other phrase is also okay.
In this context, I actually prefer
'the highest level of education of women in Someland'
One reason I like this phrasing is that it can have the meaning:
'the highest level of education achieved by women', and that seems to be the exact meaning in the pie charts: what is the highest level of education achieved by or held by women in 1945 and in 2005.
'the highest level of education for women in Someland'
'the highest level of education with regard to women in Someland.'
So that is also okay in this context. But to me, it is perhaps not as strong a statement as the first phrase.
In fact the second phrase can (but does not have to) mean
'the highest level of education available to women in Someland'. And we know that just because something is available to someone, it does not mean that they will take advantage of it. You can lead a horse to water but you can't make it drink. But in the context of the pie charts, this is not the meaning.
So again, either phrase is fine. I prefer the first one. Some people may not like the first phrase because of the repetition of the word of in it. But sometimes one cannot avoid repetition. (EDIT: If you really wanted to get on someone nerves, you could say 'the highest level of eductaion of women of Someland' - ha). Both phrases are natural, common, and contemporary.
I am curious who told you to make the "correction" and why they told you that. Was it a native speaker? It was your teacher, just make the change because that is what they think is better.