What's the best way to comfort someone that just lost their only child?

The lady is a friendly neighbor in her mid 60's. She had already dealt with the loss of her husband in late 2020. Then just 5 days ago, her daughter (and only child) died of cancer at the age of 39. Now all she has is her son-in-law and grandchildren; a 14 year-old girl and 10 year-old boy.

The lady is refusing visits at this moment and distancing herself. She doesn't want to speak to anyone at this moment. That was her only child. What's the best way to comfort someone that just lost their only child?

What's the best way to comfort someone that just lost their only child?
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