If I am understanding right, based on this and your other posts on other threads, your chin is going limp and unresponsive then back to normal? It sounds like she may be having seizures, chins can have absent seizures where they just kind of are out of it (so not the full body shaking you would normally think of) for a few minutes then seeming back to normal. I would look at what could be causing them. What are you feeding? What food as well as any treats. What is the temp where she is being kept? if it's too warm that can cause it too. Ideally if you can try to get a video of it happening and then take her to the vet to show them what is happening.