I think part of Harley's problem is that her system may not have had time to fully bounce back from those parasites (the reason I couldn't breed her this year being she was still in quarantine). That and it's her first time having babies or slugs, so I'd expect either to be a bit difficult the first time around.
I was curious though; do unbred females generally throw slugs every season, or only occasionally?

I was under the impression that for very old females breeding them would put too much strain on their bodies? I don't know a lot about it, but I would think a wild snake would generally probably not live long enough for old age to become a factor in breeding. That female definitely shows her age; you can look at her and tell she's older.

That aside, Harley is going back to the vet in the morning to stay until she passes them all. They gave my husband oxytocin shots to give her at home, but he apparently can't do it without jerking the needle out when she twitches and nearly injecting me with it. I'd do it, but I wasn't able to be at the vet when they were showing him how, and my hands were shaking too badly anyway.