Hello,
I understand your concern.
Your sister is suffering from Typhoid fever as you mentioned her Widal is positive.
The doctor has advised stool examination because bacteria causing typhoid, travels in the intestinal tract, in simple language in your stomach.
Next Steps
Listen to your doctor and get the examination done.
Health Tips
1. Avoid taking outside food or water.
2. Have plenty of water.
3. Complete bed rest.