Sonia is the current replacement for Roseanne's Research, which has rotated out of the standard format. This supporter card fills in the niche pretty nicely, although not quite a well.
However, since there is nothing similar in the format, which can fetch basic Pokemon or energy cards, Sonia does become very valuable until something else comes out in the next expansions.
If you want to invest in Sonia, then do it now. The price situation may change as soon something better appears in the format, which probably won't take too long.