Possibly, Howlyn didn't want to tell the truth to anyone because she knew she wouldn't live much longer. It was better to spare Alirio and the others from that cruel truth.
She took full responsibility for taking care of that universe in Darian's absence, since Lucy, Lucius, and all the other strongest and most reliable figures had become immortals. Without Niara to open the portal and bring them physically, none of them could use the altar of Heaven's Will to reach that universe.
Howlyn had to communicate with them through weaker Spiritual Guardians who came there. Alirio, being the son of Veyle and Lucius, was the person she trusted the most and the one who had the most contact with her during that time.
During the first assault of the Celestial Shadow, after it recovered, it wasn't simply expelled from the galaxy with a resource-burning tactic.
