Her genome did not have a small component of mixing.

It was the mixing.

Half Neanderthal, half Denisovan, with no prior admixture in either lineage — a genome that was, at the molecular level, the perfect record of a single specific biological event: the fertilization of a Neanderthal egg by a Denisovan sperm, approximately 90,000 years ago.

There is no other interpretation of a 50-50 split in a nuclear genome.

There is no statistical artifact, no bioinformatic artifact, no alternative explanation that produces that result without invoking a first-generation cross between two distinct lineages.