How do you catch creselia in Pokemon pearl after it runs away?

DON'T fly towards it.

1) Teach one of your party Pokemon mean look or block or an ability that prevents Pokemon escaping.

2) Save the game

3) Fly to Jubalife over and over (even if you are in it)

4) Use mean look so she can't escape.

5) Attack her (False Swipe's a Good Move)

6) When her health is low use a pokeball

If she faints turn off your DS and repeat steps 3-6.