Sometimes or often?

Choose the word which has the same meaning as the underlined word.

The woman had some friends, who occasionally invited her to a small party.
A. often B. rarely C. sometimes D. usually

I know the answer is C, but wouldn’t often do for this?
If you don’t accept “who often invited her to a small paty”, what is the reason?

Thanks in advance!

Good morning Rei. The answer is in the frequency of the invite.

Often is regularly.

Occasionally is sometimes.