I think Lacus just got tired of Athrun's indecisiveness.
Anyway, I was looking over the GundamOfficial timeline, and they really went through lots of time skips and out of order in some cases.
Ex:
04/17 - Strike vs. Aegis
04/18 - Athrun found
04/21 - Malchio brought Kira to Lacus's house
05/05 - Kira stole the Freedom
05/08 - Kira arrived at Alaska