Lilith didn't stop because of her short exchange with Roy. Next, she continued to wander around the various human countries and controlled the monarchs and nobles under them.
A small portion of these controlled monarchs and nobles had the bloodline of the first-generation nephalem. After learning from Uldyssian's lesson, Lilith directly adopted a compulsory control method. She used the power of her bloodline to make these monarchs and nobles unable to resist her orders and requests. Even the first-generation nephalem were like this, let alone the ones with lower bloodlines.
Lilith's army was quietly growing. After she crushed the Demon Eye, Roy didn't continue to track and monitor her. After all, he was only confirming if she had really arrived. Now that he had confirmed it, there was no need to annoy her.
He was only summoning and expanding his army while watching the development of Sanctuary.