。
She doesn't understand what I'm saying either.
Literal
She [also-も] I [possessive-の] am-saying thing [object-を] has-not-understood.
A relative clause (私の言っていること — 'the thing I am saying') functions as the object of 理解する. The nominalizer こと turns the clause into a noun phrase. The negative ~ていない indicates an ongoing state of non-understanding. The も suggests others also don't understand, and she's another one.