[ElaineM]

Kidney or bladder issues can be a side effect of some drugs. She may be taking medicine that has diuretic qualities neither her doctor, you or she are aware of. Call the doctor's office to report the problem and ask for advice about this.
Some foods can do this. She may also have a urinary track infection. She can ask the doctor for a urine test for that. If it is positive the doctor can prescribe medicine.
Cranberry is a well known home remedy for urinary track infections. I don't know if it is available in India, but it comes in juice, fruit or supplement form in the United States.
If she has a urinary track bacterial infection she should drink more water. She may not want to do this, but water helps to flush bacteria out of our bodies.