Hello Mary,
Welcome to our Internet family. I had never heard of that product before either, so I had to look it up. Apparently their sales rep did a good job with your PCP.
Their website appears to be mostly a collection of smoke and mirrors designed to make the product appear to be terrific without actually revealing what it is made from. But if you wade through the "Medical Professional" information, you can see that basically the product is nothing but a beef protein supplement. Their description of it as a "medical food" makes it appear more sophisticated than that of course, but basically, as far as I can tell, it's nothing more than a beef protein supplement made from the lymphocytes and other glycoproteins (immunoglobulins) found in the plasma of cow's blood. Immunoglobulins function as antibodies or receptors in immune system responses. They apparently use fresh blood, because after clotting, the serum no longer contains lymphocytes (or platelets) as plasma does, so they couldn't legitimately call it "serum-derived" unless the blood is unclotted. Here's how they actually describe it:
EnteraGam® (serum-derived bovine immunoglobulin/protein isolate, SBI) is a prescription medical food product intended to provide for distinctive nutritional requirements that are unique for the clinical dietary management of specific intestinal disorders [e.g., in irritable bowel syndrome with diarrhea (IBS-D), inflammatory bowel disease (IBD), and HIV-associated enteropathy]. EnteraGam®, as a medical food, must be used under physician supervision.
http://enteragam.com/
I'm not sure what "distinctive nutritional requirements" the product resolves, but for all I know, it may be the greatest product since sliced bread. However, as you noted, it is not a bile acid sequestrant, nor is it even distantly related to cholestyramine, nor will it in any way function similar to cholestyramine. Your doctor can call it "natural" if she wants, but it is a very highly-processed product, so calling it "natural" requires a stretch of the imagination. The only natural thing about it is that it's made from a natural product, namely cow's blood. The processing of course is very unnatural.
If you're not sensitive to beef, it shouldn't cause any adverse reactions, but I would be surprised if it provides any magical curative properties. At any rate, if you have a bile acid malabsorption problem, that product will definitely not address it.
I agree with you — your doctor kind of sold you a bill of goods there, and in the process she proved that many drug company reps are great at their jobs.

But who knows? There's always a chance that it might help in some way.
Personally, I prefer to get my beef protein by eating beef steak. Old timers here in the South will point out that beef blood makes good feedstock for making stinkbait to be used for catching catfish (which are also a preferred source of protein).
It's good to see you posting. Again, welcome aboard, and please feel free to ask anything.
Tex