Aries lit up as well after you retraced it the second time, it would indeed do even if the last line isn't as perfect as you wanted it to be.

Now both Sagittarius and Aries are lit up, but even with two alight, nothing is happening. Seems like you will need all three Fire Signs to unlock the cage.

As you carefully finish tracing Leo, it too lights up and after a few seconds, the constellations turn green and a click is heard as the lock unlocks and the door starts to open.

Congratulations Mr.Kenning!

You have unlocked the cage and freed your mother. However due to the extreme temperatures, she is still frozen with cold and can't move. Best start warming her up and get her out of the cage.