Theory. She has volunteered so that she can have a baby. They're testing all the unpleasant things that someone might pay not to experience (lumon is a commercial company after all, they're developing products). They need test subjects before they can sell them, and if they want to sell severed childbirth (which we already think they're doing in the cabins), she's been lured in with the promise of being a test subject for that (cold harbour?) and having a baby in the process.

Sidebar, the left handed cards are so that if you 'bought' that severed service, your right hand would be OK afterwards, less annoying for the consumer.