Well, we will never know Sinkov.

Without doubt she pushed for greater integration and for the EU to become bigger. Her aspiration was that Eastern block countries would join the party - which subsequently came to pass.
There were bound to be disagreements in the details - on many sides - but if Thatcher had been in power in the 90's she would have been pushing for EU expansion and greater integration - this is what she believed in.
And in most ways the EU today is pretty much what she wanted.
To say that she would be 100% against the EU today is wildly inaccurate. She was a committed Europhile, but she would have been pushing the UK's interests strongly as well.