Hmmmm.....I never saw this original thread or I would have commented. This is a big topic, but I'll try to make it simple here.
There is no relationship between enlarged platelets and anemia. I'll paste some links below for further reading.
Basically, platelets have to do with the clotting ability of blood. Low platelets (not the CKCS kind which is a benign anomaly) cause thrombocytopenia - a decreased ability for the blood to clot. This can result in a dog bleeding out so it is dangerous. Often true thrombocytopenia is an immune disorder but it can also be caused by things like rat poison or tick borne diseases.
Red blood cells are related to anemia - too few red blood cells cause anemia and symptoms are weakness, poor appetite, etc. Anemia can also be autoimmune (IMHA - immune mediated hemolytic anemia) or can be caused by a diseased spleen or loss of blood and is also a complication of kidney failure (the body stops producing red blood cells). Anemia can be caused by not enough red cells being produced or by too many red blood cells being destroyed. You can read all about it in the links. There aren't good treatments for IMHA (I lost a dog to that a couple of years ago). Transfusions only "last" for a few days. Giving EPO can help reverse anemia but there are usually complications - very long topic. Steroids (prednisone) are given for suspected IMHA or immunosuppressants like cyclosporin. These drugs can help stop the body from destroying its own red blood cells.
The blood test that measures these components is a CBC - complete blood count. This test shows hematocrit (HCT) or packed cell volume (PCV) which is what tells you if a dog is anemic. 33 is not terribly problematic. My girl that died had an HCT of 15, and it was acute anemia. Under 20 is dangerous - even more so if it is acute (sudden in nature) rather than chronic (slowly progressing, as happens with kidney failure). My Cavalier with kidney failure lived for two years and did quite well with an HCT that stayed in the low 20's (his was chronic), and he died at 16 for reasons other than kidney failure. CBC also measures hemoglobin, red cells, white cells (they fight infection) and platelets.
http://www.cloudnet.com/~jdickson/imhaitphandout.htm
I usually don't like to use links relating to humans, but this is a good explanation of red cells, white cells and platelets:
http://www.lef.org/protocols/heart_circulatory/blood_disorders_01.htm
Now - relative to Sadie:
Are you in the U.S.? Where do you live?
I would consult a board certified internal medicine vet specialist for optimum diagnosis and treatment planning. This is beyond a GP vet.
Can you get a copy of her CBC so you can see all of the values? Another test can be done to show if the anemia is regenerative or not.
The spleen and red blood cells are linked (read the links). If she has cancer just in the spleen or a benign tumor, a splenectomy could be done as that organ is not necessary for life. Good link:
http://www.marvistavet.com/html/body_splenic_masses.html
An 8 year old with a slight murmur can perfectly well undergo surgery, but you need a specialist. (I've had a 14 year old with more advanced heart disease have a successful cancer surgery and he was fully recovered within days - but a specialist handled his care. I've had several older Cavaliers with heart disease do quite well with various surgeries - spays, mastectomy, removal of eyes, etc.) This of course is a personal choice and there is not a right or wrong answer with a decision about surgery, but you should know that this absolutely is an option and you've been given incorrect advice if you've been told that Sadie is not a candidate for surgery.
Pat