Check out this site, it will give you some great information on reptile spays: http://www.lbah.com/Reptile/iguana_spay.htm
If your female is gravid and you do not mind her being spayed (instead removing the eggs but leaving the ovaries and uterus)the the surgery is really really simple and fast. Your dragon and your vet should have no problem. the fluid in the cavity in mot a common thing with dystocia though. There is a possiblility that an egg has actually escaped into the coelomic cavity. The decomposition of the egg would then account for the fluid. Did your vet x-ray after he removed the fluid. A fluid filled cavity can make it very hard to distinguish oragans and debris in the body cavity.
Also, your vet could first attempt to extract the eggs through hormonal injections. Oxytocin can work in reptiles with about 50% success in dragons if administered within the first couple days of the onset of dystocia. Another hormone called arginine vasotocin is even more effective but it is not likely to be something your vet has at his clinic. It is extremely effective in treating dystocia in lizards.
Fluid in the coelomic cavity can indicate all kinds of things. Cancer in the body cavity can cause it to become fluid filled, an ovary that has become twisted and lost its blood supply can cause a fluid build up.
There is also the possibility of an abcess. Has she had any wounds? Neoplasms other then malignant growths could possibly be the cause.. Without x-rays I don't think that anyone can really help you. You will have to trust your vet.
If it is a reproductive problem your dragon has a good chance. If it is a neoplasm then if it is not cancer the results are very good. There are also some viral infections and parasites that can cause abcesses in the body cavity...
What is your reason for not relying on your vet in this situation? Do you not feel comfortable with him? Is there another reptile vet in your area for a second opinion? The vet is really the only person that can help you in this situation, but if you don't trust this one there is always another one somewhere..