I was curious to see the Mexican/Spanish fansite for the Wonder Girls. ^^ I found an interesting article. I guess learning Spanish in school is somewhat of a help since I was able to guess that the title of the article was "Wonder Girls and Lim were already friends?" My sister was able to translate most of the article for me since she's taking Spanish. ^^
After news came out that Lim was a new Wonder Girls member, fans started digging information about her. The result was that Lim and the Wonder Girls had known each other for a good amount of time.
Various fans found a video of the surprise celebration of Yoobin's birthday around the time of "Tell Me". In the video, you can see very clearly Lim at 1:41 celebrating with the Wonder Girls and the rest of the JYP family. (Note: This is the original author's -- [@Wonder Fanáticos] opinion.)
cr: cutegiurlsubs @ youtube
Although we don't know how close the Wonder Girls and Lim are, they seem very comfortable together and it doesn't look like Lim is just a stranger to the Wonder Girls.
The original author's opinion (@Wonder Fanáticos): Lim was probably imagining that she would be doing more things compared to celebrating birthdays with the Wonder Girls.
Source: Wonder Fanáticos