zForget the crickets, do meal worms and like 2 waxies a day. Keep her apart from any other leo until she is up to weight, as that can cause stress and food wars.
Do not feed just waxies, as they are unhealthy and fattening, as well as addicting. Breaking an addiction is tough, and takes some time, so don't mess with it since she is already under weight.
Make sure to dust with D3/Calcium. Is there a reason she is underweight? Possible parasites or a disease? You might even want to consider a vet to just rule out all diseases and make sure it is truly just underfed.
My other suggestion, join a reptile forum, as you will get 10 times better responses from them then you will on here, as this is more of a fish forum. I've got my own forum down in my sig, you can try posting there, they helped me out with my issues, and thegeckospot.com is decent too, but I didn't have the best of luck with them all the time.