I'm pretty sure you just have to invite Beth over or hang out you know where you choose between the three main girls and if your at that stage it should prompt a unique event where you bring it up and get the item. Might be wrong though
you have to go to the running path at weight stages 3-4 to get Beth's number, if she is in your contacts you can call her to help with Lilly. If you are too overweight already you will no longer be able to get her number
