Why did her lineage not survive to the present?

The evidence does not conclusively answer this question.

Several scenarios are plausible.

Direct replacement is one.

Later waves of modern humans with different genetic signatures — populations from different source regions or with different ancestral compositions — could have expanded into central Europe after Zlatý kůň’s time and replaced her population, through demographic expansion, technological advantage, or simply higher reproductive rates.

Population collapse is another.

The climate fluctuations of the Late Pleistocene were severe and frequent.