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You need to see a vet with her. Because she is young and it has come up so quickly it is likely this is something that can be treated. It is likely an abscess in the pouch or possibly in the tooth root or even a cyst. It is likely painful and would need drained and flushed and then antibiotics but she should recover well. Offer some soft foods like babyfood and porridge so she gets some food in her. Does she chew the water bottle spout at all? It could be a pouch full of water! If she does chew then take the bottle off and replace with a small pottery bowl for now