My aunt is trying to steal the inheritance by trying to get close to my grandmother, how can I stop her?

My grandmother will not live for much longer. At first, she was going to pass down the inheritance to my father. But my aunt suddenly started spending a lot of time with my grandmother, pretending that she regrets not spending time last time. She is not working, so she has time to visit everyday. Unfortunately both my parents are working, so they don’t have much time to spend with my grandmother other than weekly or bi-weekly visits. My father is also too nice to confront his sister about it.