Give her one of those whole tablets now, then once daily for a week.
See if she's able to expel an egg. You want her to have the whole tablet.
Pull down on her Wattles to open the beak, pop the tablet into the beak and let her swallow.
She's young, so this is not a great start. See that she's eating/drinking o.k. and that she has a nutritionally balanced poultry feed to eat. Provide oyster shell free choice.
A White Leghorn is generally a very productive bird and they need oyster shell and a good complete feed. I'd aim for an 18-20% Layer or All Flock feed.