Actually, it's the same number of the people who follows you...
If you are not a member of twitter, but read someones tweets is it anonymous?
Yes anybody can read your tweets. Twitter is a big great tool.
If your tweets are protected then only people following you can see your tweets. If she isn't following you then maybe she has access to an account that is following you.
You can't sadly.
If you protect your updates, the people who follow you CAN see your tweets, but ONLY the people who follow you.
Twitter is a web-site; anyone can go to that site and read what has been posted. Your tweets go to the world.
All of your tweets are stored on your time line, similarly your @replies are also stored. Go to your profile to read all your tweets and go to your @replies to read those from others.
There is no way of knowing who has visited your profile/read your tweets.
You can tweet about anything, there aren't any "set" tweets that people use.
You can see how many tweets you have posted by going to your profile. There is a total number underneath your number of followers/people you follow.
You will receive tweets on your homepage from everyone you follow. Unfollow them to not receive their tweets. To stop people seeing your tweets (except from those you approve) you can protect your tweets from the settings menu.
You can't. But you can block people or protect your tweets, but if you protect your tweets people can not retweet them.