I think the lovely comment by svat covers the extent of her contribution to TeX: the eqn language informed the design of TeX's math-mode syntax. But that's all I'm aware of; it seems the much-copied quote you mention is off base. Keep in mind that TeX was initially written in Sail, which had no Unix compiler, and also assumed 36-bit words, which no Unix system had. The later rewrite of TeX that ran on 32-bit machines, and finally became available on Unix, pretty much retained the Sail version's existing math syntax.