Dear Sally,
I am happy to get your letter,but I am really sorry to hear that.First of all,I think,you should tell yourself that she is not your friend,she can be everyone's friend.Second,even if she has a new friend ,she is still your friend.When she has a delecious cake,she will be also glad to give some to you.Last, you can also to make some new friends.
And i really hope that you can be happy.
Yours
Lucy.