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

You don't seem to think! No one thinks-- no one knows how I feel.

VOA: special.2010.05.15

"If you get a doctor who is away in the village and has come across a case he or she thinks is beyond him or her, why cannot that doctor be able to link up easily with a senior doctor in Korle Bu to get advice on it?

VOA: special.2009.06.17

Now,he thinks short is better. "I've gotten researchers telling me that you don't realize is how long someone can have a high level of concentration.

VOA: standard.2010.03.26