Dany will feel like she's the people's joyous messiah saving them from the awful grip of tyranny, by arriving at Westeros with 3 weapons of mass-destruction and a horde of Dothraki rapists and murderers. She'll be seen as a major, evil threat, and be swiftly shot down by the combined forces of Westeros.
Assuming she somehow manages to get her dragons to behave. Meanwhile, she only has one.
Also, how will she get to Westeros? Moving thousands of people and all the needed equipment to other continent is an enormous logistical problem.