Praise be to Allah.
Since using this water is not a means of healing, whether according to sharee’ah or science, then using it is a form of minor shirk, because minor shirk means using as a means something that cannot be a means.
What this woman should do is to recite ruqyahs for herself that are prescribed in sharee’ah, such as al-Faatihah and al-Mi’wadhatayn (the last two soorahs of the Qur’aan), and there is nothing wrong with seeing doctors to treat her problem.
We ask Allaah to heal her.
And Allaah knows best.