please someone tell me how to get latias after you've already seen her..

All you need to do is go to the safari zone and search in the grass neer it and only that grass it might take a while but you should run into her.

1) Go to a place where she appears quite often.

2) Check your pokedex to see if she is there.

3) If she is there you can catch her.

4) If not save your game and reset (A+B+start+select all together).

5) When you continue check your pokedex if she is there.

6) If she is not there now repeat step 4 untill she is.

P.S. I did not invent this someone else on this wonderful site did

To catch Latias, you have to surf into the middle of route 130 and save the game. You then check the area of it and if it is not in the area just restart the game and try again.

It may take a while but don't give up-for all you know it may only be one more restart before it appears on route 130.

Think back to the simpler Pokémon that you probably found elusive but consulted the Area tab in the Pokédex.

It's the same thing with Latias and Latios, as with Raikou, Entei, and Suicune in the previous versions: They are recorded in your Pokédex and their area graphed.

As you move form locale to locale, so will Latias or Latios, so ensure that he or she is a decent distance away and try to progress toward them. Latias appears on all routes except 101, 102, 103, 104, 105, 106, 107, 108, 109, 112, 113, 114, 115, and 116, and sometimes it can appear at the Safari Zone.