Hello,
Thanks everyone for your thoughts. I'm sure other readers found them as interesting as I did, and will benefit from your combined wisdon.
I, however, was not able to implement any of your ideas. There just wasn't enough time to regroup. The reasons are many.
I had overextended my forces in taking out two AIs, the XiChung and the Uruk-Tal. At the same time, I had skipped a generation of new ships, instead stupidly building a bunch of value-improvement facilities. So I was using older cruisers and battlecruisers -- not to mention a bunch of clearly obsolete light cruisers and destroyers -- when my human opponent had been building top-of-the-line dreadnoughts.
Even though I quickly realized my mistake when I came up to her border (which is when I posted my original plea for advice), she moved too quickly, taking two systems every two or three or four turns with multiple, large fleets of her lethal dreadnoughts.
My infrastructure wasn't all that great, and production grew worse as she moved forward.
Two other AIs chose this time to send in big fleets across my eastern marches and into my core systems, where I had gutted my defenses, transferring the ships there to the southwest to try to slow her down. The AIs didn't attack my planets, but their mere presence decreased production.
It was interesting, as well as frustrating, to experience a rolling collapse of the mood on my planets as she came on. At the end, I had around 50 or 60 planets rioting at the same time.
If we play again, I'm either not going to let her have the religious trait or I'm going to have it, too.
Well, OK, that's just sour grapes. If we do play again, I'm going to be less interested in expansion for the sake of it, and try to keep up a steady stream of ever-more-modern ships.
In the end, I should have known I was in trouble the minute she chose the Borg shipset.
Again, thanks everyone.