Her high amount of matches means she comes from an endogamous population. Many Euroamerican populations share that characteristic and of course the Ashkenazi Jewish population is notorious for it.
But Ashkenazim do have many more matches with trees than what our JD has.
She is from an endogamous Euroamerican population, maybe German American.
Fwiw, found this interesting explanation..
Concepts – The Faces of Endogamy | DNAeXplained – Genetic Genealogy (dna-explained.com)
''Endogamy and Genetic Genealogy
In some cases, endogamy is good news for the genealogist. For example, if you’re working with Acadian records and know which Catholic church your ancestors attended. Assuming those church records still exist, you’re practically guaranteed that you’ll find the entire family because Acadians nearly always married within the Acadian community, and the entire Acadian community was Catholic. Catholics kept wonderful records. Even when the Acadians married a Native person, the Native spouse is almost always baptized and recorded with a non-Native name in the Catholic church records, which paved the way for a Catholic marriage.
In other cases, such as Justin’s admixed group, the Brethren who notoriously kept no church records or the Jewish people whose records were largely destroyed during
the Holocaust, endogamy has the opposite effect – meaning that actual records are often beyond the reach of genealogists – but the DNA is not.''
A fully endogamous Jewish individual’s most common surnames are shown above. If you see Cohen among your most common surnames, you are probably Jewish, given that the Kohanim have
special religious responsibilities within the Jewish faith.
Of course, especially with autosomal DNA, the person’s current surname may not be indicative, but there tends to be a discernable pattern with someone who is highly endogamous. When someone who is fully endogamous, such as the Jewish population, intermarries with other Jewish people, the surnames will likely still be recognizably Jewish.''