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.
That girl should not preoccupy herself with the answer of that woman; we fear that her question stems from whispers.
There is no doubt that the statement of that woman is falsehood if she meant disbelief according to the terminology of the scholars. Disobedience to parents, even if it is a lack of dutifulness and obedience to parents, it is not disbelief.
For more benefit, please refer to Fatwa 13087.
Moreover, obedience to parents is not required except in what is permissible.
For more benefit on the limits of obedience to parents, please refer to Fatawa 271255, 131695, and 123554 and 401131.
With regard to the ruling on mixed studies, please refer to Fatawa 363820, 82730, 87310, 128402 and 84563.
Allah knows best.