I think that usually has a lot to do with what they actually tweet. If she only promotes lesser known shows of her friends or basically sends the same tweet about Celebrity Name Game every other day (only with altered guest star names), people just don’t like/retweet that kind of stuff cos it doesn’t directly involve her.
Pictures, on the other hand are an entirely different story. Be it facebook, twitter etc - people are more likely to like/comment/retweet/favourite actual photos.
So I’m not sure if it has something to do with her general ‘popularity’… (/end of online marketing intern rant)