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.
It is permissible for a breastfeeding woman to break the fast if she fears for herself or for her child or herself and her child together; in this case, she is only required to make up for her fast, and she does not have to expiate.
Sheikh of Islam Ibn Taymiyyah, may Allaah have upon him, said in the book Al-Umdah: If she fears for herself and her child, then she is not obliged to expiate based in the analogy to the words of those who do not necessitate it due to fear for the soul.
If the questioning sister breaks her fast out of fear for herself and her child -as mentioned in the question- she is only required to make up for it, and no expiation is required; this is our view in the Arabic section.
Allah knows best.