If your friend cannot stop talking about something because she thinks it is important, you might say she has a bee in her bonnet.

VOA: special.2009.06.28

Ready to go! Fired up! Ready to go! They cannot stop us.

VOA: standard.2009.09.12

"We cannot stop terrorism or defeat the ideologies of violent extremism when hundreds of millions of young people see a future with no jobs,no hope and no way ever to catch up to the developed world,"

VOA: standard.2010.01.06