This is fairly common with some pet birds – both males and females. Many just regurgitate, but some will eat it and often regurgitate again. It’s not ideal because it can cause some irritation in her crop and throat, and it can cause some loss of nutrients. For whatever reason, the placemats are triggering her hormones, so I would keep her off of those. You mentioned she isn’t doing this when you are around, so does that mean you allow her to roam at will? This can also cause a female to want to nest and end up laying eggs. It’s best for her to only be out when you are interacting with her, or she needs to remain on the cage or on a playstand. Roaming makes her feel like she is looking for a nesting spot.
Thank you for asking Lafeber,