first off testosterone is not a must...at all
second, as far as fat burners go.. in my honest opinion, i don't believe they are.. i believe as long as your diet and training are spot-on, you'll do fine.. it's not until you want to compete/get into the low bodyfat %'s that you'll need hardcore supplementation...
a main factor with this, though, is if the individual has any health issues that might prevent her from getting "fit" like thyroid disorders and such. then some help (medical help, that is) is needed. but if you're a healthy girl there's no reason you can't get hot and fit with strict diet and hardcore training.