This is a challenging situation for everyone involved! Try replacing what she's chewing on with something that is okay. It could be that she has some "sensory issues" and she needs to chew on something hard or chewy to fulfill a need she has orally. (For example, if I eat a lot of soft foods in a row, I notice that I crave something hard, crunchy, or chewy to eat. Even if I am not hungry, I will continue to pillage until I find the food that meets my physical need. Some people are a salty or a sweet person and they need that to fulfill a need.) Maybe she is like this. Or do you notice that it's her way of getting your attention? Maybe it's because your 12 month old is taking time away that she is wanting and this gets your attention. Try watching when she is doing the chewing ( time of day, what's going on during that time, etc.) and see if you can include her in something then, or make some special time for her alone. Good luck!