She could have been talking double Dutch for all we understood of it.
Origin of double Dutch
noun, (sometimes lowercase)
a form of the game of jump rope in which two persons, holding the respective ends of two long jump ropes, swing them in a synchronized fashion, usually directed inward so the ropes are going in opposite directions, for one or two others to jump over.
Language that cannot be understood, esp overly technical jargon: Plain English will do; cut the double Dutch
[1864+; Dutch, ''German,'' being unintelligible, double Dutch is twice as opaque]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with double Dutch
Language that cannot be understood, gibberish, as in They might have been speaking double Dutch, for all I understood. This usage dates from the 1870s (an earlier version, however, had it as high Dutch) and is heard less often today than the synonym double talk
A game of jump rope in which players jump over two ropes swung in a crisscross fashion.