Yes, there might be more. "Egg-bound" is when they DON'T come out, & rot inside the snake (with negative health consequences).
Not sure a "soak" will help, but some swimming in shallow barely-warm water (like in your bathtub, where she can stretch out) might help- it helps for constipation, anyway, not sure about slugs, but it couldn't hurt- so I'd say it's worth a try.
The hydration helps anyway- my rat snakes soak in a large water bowl for 3 days solid after they lay eggs, before they're ready for food. I don't offer food until they leave the water on their own.
Yes, maybe this is why she's off food- does she still have a nest box? If you took it away, that won't help...I'd give it back. Yes, slugs can be passed later (like 3 mos.) but it's always best to have all eggs & slugs laid at the same time.