Yes, her breast cancer is said to have been caused by her constant worries
The cancer she died from was liver cancer that had spread from her breast cancer to the liver
I see this is confirmed in many scriptures, have you found verses in the Quran in support?
Here are a couple of Baha'i Writings that confirm mental aptitude is an aid
Bahá’u’lláh says:—
"Verily the most necessary thing is contentment under all circumstances; by this one is preserved from morbid conditions and lassitude. Yield not to grief and sorrow: they cause the greatest misery. Jealousy consumeth the body and anger doth burn the liver: avoid these two as you would a lion". (Tablet to a Physician)
And ‘Abdu’l-Bahá says:—
“Joy gives us wings. In times of joy our strength is more vital, our intellect keener. … But when sadness visits us our strength leaves us.”
‘Abdu’l-Bahá writes of another form of mental healing :—
"that it results from the entire concentration of the mind of a strong person upon a sick person, when the latter expects with all his concentrated faith that a cure will be effected from the spiritual power of the strong person, to such an extent that there will be a cordial connection between the strong person and the invalid. The strong person makes every effort to cure the sick patient, and the sick patient is then sure of receiving a cure. From the effect of these mental impressions an excitement of the nerves is produced, and this impression and this excitement of the nerves will become the cause of the recovery of the sick person. (Some Answered Questions, p. 294.)
I see It would be good for you to share some Muslim thoughts on healing.
All the best, regards Tony