[quote name='ihadFG']It's been a long time since I played it, but I'm pretty sure I did the combination attack with the rock crusher before taking out the towers. Once you kill as many things as possible, then you can take out the towers and open up the bridge.[/QUOTE]
Just take all of the towers on your side of the bridge, then put a lot into building the crossbow cars and riding them across the bridge with Eddie. As long as her more advanced units aren't on the bridge at the time you can usually get across and get a lot of attacks in on the stage. Should be able to keep doing that and win before she takes out all of your towers and the stage.
Sadly that worked for every battle in the game on hard.