For a 1-1/2 year old bearded dragon, I think hornworms are pretty healthy. They are lower in fat than crickets, Repti-Worms, and waxworms. They have a great calcium to phosphorous ratio (1:3), too. You do still need to dust them with calcium. The only concern I would have is that they are low in protein, but your dragon isn't growing, so I think a lower protein feeder is fine for an adult. They have 9% protein, compared with Repti-Worms at 9.4% and crickets at 21%.
So if you are interested in their nutritional value, I think they are great.
BUT...I agree with Brandon. A varied diet is best. It can be very stressful to worry if you can't obtain a certain feeder. Then again, you've tried the tough love for a month and she didn't eat anything, right? So if you can't get hornworms for a while, she will just go without or learn to eat something else.