Excess of anything is harmful. First restrict watching time. If tearing is reduced after this, simply excess strain is the issue
If any refractive error present, such symptoms are common. Check eye sight. If needed glasses could solve her problem. Need consultation. Or check her vision by online tests.
At 66 reduced vision due to cataracts could also lead to eye strain, causing tearing.
Next Steps
when was her eye examination done
Health Tips
eye check up would easily find her problem.