It is normal for your PC to not detect the device in the "usual" way when it is in bootloader... but if you go into Device Manager you should see a device called "Microsoft USB Sync" under the "Windows CE USB Devices" heading.
The fact that the PPC screen changes to "USB" from "Serial" when you plug it in means that it's seeing the computer just fine. But bootloader mode doesn't trigger activesync so maybe that's what is fooling you.
I would suggest just running the latest official ROM update package from your carrier (you can download it at
www.utstar.com). That should re-flash all 3 ROMs and get you back to a "known good" configuration.
Then you can try to flash the custom again (and this time keep your daughter away from it
)