The photos and tutorial linked below, shows how to give oral medication.
For giving a tablet, you can just pull down on the wattles, open the beak and pop the pill in, let the hen swallow...
I'm sorry she's not doing well.
Sounds like she may be having a hard time passing some material from the oviduct.
I'd give her 1 Calcium Citrate with D3 tablet now, then another in 12hrs, then once daily for a few days.