I was able to feel the tumor, but it was quite small. Smaller than a marble... maybe just a little bigger than a dried pea. I thought it was something in the crop, but it was actually next to the crop (and putting just enough pressure on the crop to slow his crop down). But I must stress that every bird is different and it can really do different things in each bird.
He also had the tumors on the walls of his heart and through one ventricle, so when he would bend down especially, he'd get light hearted and seem woozy. A few days later he started panting for breath and his comb turned that terrible purple color. His heart was failing. The timeline might be different for other individuals.
Marek's can also cause other irregularities in the digestive system, most commonly the proventriculus, and abnormalities of the gizzard. Many find that the crop may be similarly effected. Her poop still looks fairly normal right? How much is she eating and drinking on her own for you?