解釋文法Nadia always writes in...

Question

一.Nadia always writes in her diary before bed.
我不懂 writes 後面為啥要加 in ，writes her diary 意思就是寫她的日記，為什麼要加 in？
二.請幫我看下面3題的文法有沒有錯:
1.I ran into a good friend of mine on my way to the bank.
2.The girl is talking with John whom is my girlfriend.
3.Be sure to keep in touch with me when you get there.
謝謝!

Answer 1

1.
寫日記要說: to keep a diary, 不是 to write a diary
to write in her diary: 在日記本裡寫(一些東西)
2.
第二句改為: The girl talking with John is my girlfriend.