All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If by going to the graveyard, you mean visiting the graves in order to be admonished and take heed and not to seek blessings from the grave or to get closer to the dead person by offering acts of worship to them, then the view we adopt in our site Islamweb is that it is permissible for women to visit the graveyard for admonition (to take heed).
However, if going to the graveyard is for a forbidden matter, such as seeking blessings from the dead person or supplicating next to his grave while believing that supplicating Allah there is better, then this is an innovation in religion and it is not permissible for her to go with them as long as they go for this purpose because this involves witnessing evil.
It is even more forbidden if going there is for the purpose of asking the dead in the grave (to fulfil their needs), or to slaughter to him, or to devote any act of worship to him, as this is major Shirk.
It is obligatory for that girl in both cases –whether they wanted to do an innovation or Shirk –to forbid her family from evil and to advise them as a way of fulfilling her obligation of enjoining good and forbidding evil.
If her family insists after she advises them, then she is acquitted from sin but she should not go with them.
If they force her to go and she cannot repel them or avoid this, then she is not sinful, as the Prophet said: “Allah has forgiven my nation for things they forget, or do by mistake, or are forced to do.” [Ibn Maajah and Al-Haakim]
Allah knows best.