How can I get my hair like Georgie Thompsons'.....? (picture)?

This is called a root-stretch. If you already have brown hair we would just backcomb the roots and lighten the ends so that the colour is shattered down from the midlengths to the ends. This is a very popular colour at the moment and any decent colourist should know exactly how to create this style. You wouldn't necessarily need to use extensions, but that could work too.