If someone remarried without first getting a declaration of nullity, but after her second marriage her first spouse passed away, does she still need an annulment or can she receive the Eucharist without it?
Assuming this individual is a Catholic and always has been, she does not need an annulment but she does need to validate her marriage before she can receive communion.
At the time of her second marriage her spouse was alive, therefore the attempted second marriage is invalid. Once the former spouse passed away then she was free to marry, she would need to exchange vows in the Church after that point. As of now she is in what’s called an irregular marriage (i.e. an invalid civil marriage) and should not receive communion until the situation is rectified.