I found this to be the most difficult battle in my Brutal playthrough. The easiest strategy I found was to storm the fan holes, putting up booths as quickly as possible, put to use your car and zeppelin guitar cords if you need an extra boost to take some of the fan-holes over, it's worth it.
The point is to rush as fast as you can to bottleneck the enemy on the bridge. Once there it's easy to hold them off until you can store up around 2K fans, on top of a full 40 points worth of an army.
At this point, just slowly inch your group towards the other end of the bridge, then take out the towers while mounted on the giant siege tower with the turning wheel on the front (forgot the name).
When both towers go down, this map gets intense. Ophellia will send an onslaught of minions at you, mostly siege cars, and a new one, a tree. Attempt to destroy/kill as many of the group before they reach the other half of the bridge.
If that happens, refill your troops, then keep pushing them towards the opposite end of the bridge. Your goal's to rush the fan holes and stage. Using the guitar song that stops troop spawning will be a lifesaver once across, also.
Past this, just continue slamming your head against Ophellia and her new tricks, you'll come out ahead...Whether you're playing on Brutal or not.