TeWiSavesTheDay
I suppose you could argue that just being there showed that it was possible for women, but I think that's a pretty weak argument.
The Australian PM disagrees with you. From The Telegraph:
Australian Prime Minister Julia Gillard said she "changed history for women".
She said: ?As a woman, I am admiring of her achievements becoming the first woman to lead the United Kingdom, the first female prime minister there. Many around the world will be reflecting upon her life and times today, as is appropriate with the loss of such a significant figure.
"For women around the world, they will be reflecting on the loss of a woman who showed a new way forward for women and a way into leadership."
She certainly made it no easier for other women to follow in her footsteps. In some ways I think she may have made it harder.
Well, we could count the number of female leaders before she came to power, and the number after, and see whether that stacks up. Who should we get to do the counting? Merkel? Gillard? There's a list on Wikipedia of female heads of state. Putting aside the appointed (non-elected)ones ISTM that the overwhelming majority of them came to power after MT.
On that basis alone it's hard to argue that she made it harder.