Well, ya, there's nothing much you could do if one side do not put effort in keeping a friendship. I had few of those experiences. Either my friends moved away or I did. I tried on my part to write and eventually just gave up totally.

It's important not to take it personally though. I had a friend whom I stopped contacting because she did not reply me. Then after 10 years, I moved and I wrote her a postcard out of the blue, not expecting much. To my surprise, she replied and we are in touch again and seen each other few times, though we are in different countries, but closer. However that did not mean more frequent contact neither, she is just not that kind. So I just let it be.

Another friend of mine, who was very close, we used to dine and open our hearts to each other and chat till midnight. Now that I moved, she doesn't bother to keep in touch despite me writing and called her few times. Now I totally gave up.

At first it was depressing and I even get kind of upset. Now I leave it all behind. I find new friends and involve in many new things to do and life is so full and meaningful.

No, I don't think you are view as a pest if you drop her a postcard or mail every now and then. She'll reach out if she is ready for it.