Having lost my daughter, I've completely lost my will to go on.

Literal

Daughter [object-を] lost, completely heart [possessive-の] resilience [subject-が] disappeared.

娘をなくして 'having lost my daughter' — なくす used for bereavement. 心の張り 'mental resilience, emotional drive' — 張り means 'tension, tautness,' here metaphorical. すっかり 'completely.' A devastatingly simple expression of grief.