Yes, it's true about being eggbound can be fatal in 24-48 hours.
Warm Epsom salt baths will sometimes relax the hen's muscles and help them to expel the egg.
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I'm sorry about your hen. I'm going to request the mods move this to the Emergency Forum so you get more help.
From what I can tell, you're doing what I'd do but there are others with more experience there.