Understanding of Lissandra's new upcoming passive
Lissandra's new upcoming passive is as follows:
“Iceborn: When a champion Lissandra has damaged within the last three seconds dies, they become a Frozen Statue. Frozen Statues slow nearby enemies by 30 percent. After 2.5 seconds Frozen Statues shatter, dealing X (+Y AP ratio) magic damage to nearby enemies.”
So here's my question - does the champion need to be killed by Lissandra herself only before turning into a frozen statue or can this work when one of her allies kills a champion after being damaged by her within the last three seconds?