It depends on your ID number.
Go here to get the word that will make her laugh.
See related link below.
Chat with our AI personalities
You can cheer Walda up with words that will make her laugh. These words are often nonsense arrangements based on the Trainer ID.
You have to type in "PAttyPete"
Walda is at rostburo city in a house. (hint: if you see two kids at a desk you are there. Go in Rustboro from the Pokemon center to nnw and take the 2nd house and take the stairs and you found her.
There is no easy answer to what to tell Walda as the answer is based on an Individual trainers Trainer ID. The code you tell her is a mixture of upper and lower case letters that can be customize with color due to hex codes. There are many different resources that can help with the algorithm for divining the answer.
It depends on your trainer ID and usually has random characters.