Debbie Reynolds died from a stroke. This is the opinion of the medical experts. while the stress of dealing with her daughter's heart attack and ultimate death may have contributed, she ultimately succumbed to a stroke. The timing was unfortunate for her loved ones, who have to deal with the loss of two relatives.
The medical cause of Debbie Reynolds' death is listed as a stroke, she had been in a medically frail condition for more than a year. It's very likely Ms. Reynolds' stroke was the result of 'Broken Heart Syndrome' (also known as stress-induced cardiomyopathy and takotsubo cardiomyopathy), as the result of her daughter's recent death.
Did the death of her daughter possibly play a role in Reynolds' own death? In other words, can a person die of a broken heart? I think, indeed, broken heart syndrome is real and it exists. Broken heart syndrome can happen in response to any acute major stressors in someone's life.
Debbie Reynolds was likely killed by a massive stroke--after finding out that her daughter had just died. Many times older people can suffer severe strokes or heart attacks after learning about some devastating news. Reynolds hearing about her daughter, Carrie Fisher dying probably brought on the severe stroke, which took her life the next day.