Second opinions are always good, but I don't understand the guessing. If money is an issue and you are not getting the necessary tests done, then that leaves a vet hampered in making a diagnosis. If that is the case, then a second opinion is not yet in order.
I would suggest that you apply for Care Credit and see if the vet you are going to accepts it....if not, then find one who does.
CareCredit Healthcare Finance - Payment Plans and Financing for Cosmetic Surgery, Dental, Vision, Hearing, Veterinary & Other Medical Procedures You can apply online. If not, then perhaps talk to family and friends to see if they can help you out.
Good luck! Your girl definitely sounds like she needs veterinary care sooner rather than later.