Hello,
The teeth are becoming weak and small because of multiple factors involved like age,
diabetes, grinding of teeth, weak gums, improper oral hygiene methods.
Teeth do not heal or regrow like your skin or any organ in your body.
Only changing toothpaste and mouthwash is not going to help.
Next Steps
Visit a dentist to get a thorough cleaning of her teeth done, ask them about proper oral hygiene maintenance
Check for subconscious teeth grinding habits or sleep apnea.
Get a OPG(xray) of her teeth to get a better understanding of the teeth and support structure
Health Tips
Use a softer bristle brush, a non abrasive toothpaste and round motion while brushing.
use flossing/interdental brush
use chlorhexidine mouthwash
use a gum astringent to massage your gums