I got soundly destroyed by this one too initially. I think the problem mainly is that there are too many new things all at once (first time facing a non-symmetrical opponent in a full-on Stage vs Stage battle, several new enemy units, etc).
In the end I found Schafer's blog post of tips
very helpful. Particularly:
1) USE DOUBLE TEAM! + solos
2) Don't split your army.
[my caveat: except to send out cloaked roadies to take down enemy towers]
3) Be aggressive.
I found leaving troops behind to defend a point never really worked, as they would just get clobbered as soon as Ophelia dropped by... so rather than try to hold geysers I made sure I was constantly taking a new one, drawing her focus away from my base.
Also useful: strategically advancing your Summon Flag to be as close to the front as possible (and preferably near choke points).
So basically my approach was: build some troops, take them to the nearest enemy tower, claim geyser and plant summon flag - all the while building new troops and upgrading my stage - Next tower.