。
She seems to understand what I'm saying.
Literal
[topic-は] I [subject-の] is-saying thing [object-を] is-understanding [seems-ようだ].
ようだ marks an inference based on observable evidence — the speaker has watched her behavior and concluded that she's grasping the message. Compare みたい (more colloquial), らしい (hearsay-tinged), and そうだ (more direct visual impression). The relative clause 私の言っていること ('the thing I'm saying') uses の as the subject marker inside a noun-modifying clause, where it stands in for が — a hallmark of Japanese subordinate-clause grammar. こと ('matter, fact') nominalizes the verb phrase into something graspable as 'what I'm saying.'