Heidi, it very well could be hemobart, but sometimes a slide exam in the clinic lab is not enough.
Your vet knows this, but she may not have discussed in greater detail with you, so please call and ask about getting a full feline serology done to rule out hemobart, coombs, toxoplasmosis or immune-mediated anemia, lymphoma,... all of which need to be ruled out when the hematocrit is so low. Sometimes it is also necessary to include an ELISA for FELV/FIV/FIP because snap tests done in the clinic may not always be reliable, especially given her symptoms at this time.
You may have to prepare yourself for a possible blood transfusion, your vet probably has a donor-cat at the clinic for such a reason, but do discuss this thoroughly with your vet so that you are fully prepared for what to expect.
The medications appropriate at this point are heavy doses of prednisone and tetracycline, plus antibiotics, fluid support and nutritional support, until further labwork reveals the actual condition. Regardless of the blood-borne disease type, these medications are commonplace to treat blood disorders.
In advanced cases or those that the vet is simply stumped, or that serology doesn't confirm anything definitive, a bone marrow aspiration can be done to rule out different types of cancer, however, I would use this as a last resort only, it requires anesthesia, is not a comfortable procedure and in a 2-year old cat, it probably wouldn't define cancer (unless it were an inheritable-type, rare). At this point, the biopsy should confirm the lymph node reaction and determine the likelihood of cancer. But, pending the biopsy and because she is not a good candidate for anesthesia right now, I would definately opt for a full feline serolgy ASAP. This needs to be sent to an outside lab and may not get the results for up to 5 business days. In urgent cases, your vet can call the lab to get faster results. Please talk to your vet about this immediately.
Whatever she is suggesting toward treatment, or possible blood transfusion, please heed her advice, blood disorders are very difficult to treat, especially in critical cases, it must be agressive and almost impossible to predict the outcome.
Having treated such diseases, and personal experiences with them, I would like to encourage you to follow your vet's direction and not give up with treatment. I've seen severe cases improve in time and with aggressive treatment, although expensive, it is worth it to see recovery.
Hang in there and keep in constant contact with your vet. If Ginger is being hospitalized, visit her every chance you get, she needs you there as often as possible for support, for encouragement to become stronger during treatment.........................Traci