I don't know that this is the case for the lady in the article, but usually recruiters/sourcers at these companies are on contract for 12 months max, due to the hiring company not wanting them to appear as employees and thus not get full benefits.

It could make sense. I'm assuming they will be doing actual work during that time. A paid 12 month long apprenticeship would be good for both parties. It's enough time for Meta to decide if they want to hire an employee full time, and a year would give sourcers a decent amount of experience if they wanted to leave.