I'm sure that in 2015 there's lightsaber crystals available at every corner drug store, but a long time ago they were a little hard to come by.
Lightsaber color used to usually mean something. These days it's left entirely up to personal preference (in and out of universe). Gathering the crystals to create a lightsaber is the hard part. If you have them, you might as well just build a new one. AFAIK, she still has both lightsabers and (I hope) we'll learn very soon which one she prefers, in episode seven.
Creating a Meaning for Lightsaber Colors –scifi.about.com
Even within the Star Wars universe, the meaning of lightsaber colors is not always certain. Jedi vs. Sith: The Complete Guide to the Force, for example, states that the idea of lightsaber colors reflecting their wielders' personalities is a "popular notion," but incorrect. Rather, lightsaber colors depend on the type of crystals used to create the blade.
According to The Jedi Path: A Manual for Students of the Force, lightsaber colors originally indicated a Jedi's role in the Order. For example, Jedi Consulars, who focused on non-violence, carried green lightsabers to symbolize peace. Jedi Guardians, on the other hand, carried blue lightsabers as a symbol of uniformity and solidarity. These symbolic colors began around 4,000 BBY. By 1,032 BBY, lightsaber colors were still associated with different types of Jedi, but were neither required nor exclusive. Kerra Holt in Knight Errant, for example, wields a green lightsaber despite having no association with the Jedi Consulars.
The in-universe explanation for the lack of lightsaber color variation in the movies is a lack of colored crystals. According to Jedi vs. Sith, the Empire quarantined or destroyed many sources of lightsaber crystals. This left the Jedi with mostly Ilum crystals, which can only produce green or blue blades. This explains neither the dearth of colors in the Prequels nor the unusual lightsaber colors in the Expanded Universe during the time of the Empire, but it's likely the best explanation fans will get.
After reading, What is the reason that lightsabers have different colors? I can only surmise that Leia's is a natural crystal (which would make it completely okay in my book) and not a synthetic crystal.