I'll quote from Carol Ann Lee's book as this is not my area of expertise:
Vanezis recorded in his initial notes: "Bloodstained palm print on nightdress matches bloodstains appear to have been transferred from r. hand..both hands not contaminated apart from bloodstains." But in court he declared that Sheila's hands were "completely free of blood and if she'd pressed against the nightdress I would have still seen some traces of blood on her palms." He explained that blood on her nightdress "appeared to have been transferred from her wrist" although "the palm of her hand was certainly not contaminated with blood, but there was spotting of blood associated and close to the wrist."
Asked to address the discrepancy today, Vanezis muses: "I'm not sure whether I said that after the blood had been washed from her hands." Regarding his courtroom statement about the stain on her nightdress, he reflects: "The smear in the blood on her neck wounds is obviously from putting her hand up to it. Her fingers could then have made the marks on her nightdress because there are three streaks forming the stain-two together and one slightly apart. The marks could be from her wrist, but the thickness of them definitely resembles fingers and she certainly has some blood on the side of her hand. There's also a line through the streaks where the material has folded, giving a slightly distorted pattern.". The blood trails evident on Sheila's lower right arm, together with substantial bloodstaining on the right side of the nightdress in the armpit area and below, reinforced the probability that she had raised her hand to her neck."
Thanks. This, and the autopsy report, makes it unclear whether any tests were done on the blood found on Sheila. It would appear that the pathologist and the police have simply assumed it was her blood and have smoothed over that assumption.
That said, you have to balance that with what the autopsy report mentions about the loci of the blood stains: re-reading it, it does seem that the blood was only on the front of her nightdress. I think that in itself does point to Jeremy Bamber as the killer. Not that I am coming to any conclusions, but if Sheila was the killer, you would think that, at the least, there would be a struggle with Nevill, with the probability that her nightdress would reflect this: it would be torn, have Nevill's blood on it, the signs would surely be obvious.
I think Jeremy, if he is innocent, has a big problem here. Are pro-Bamber posters asking me to believe that Sheila shot everybody, and in addition to the Rivlin/Trezeon case theory that she calmly replaced the moderator back in the gun cupboard [must keep the place tidy!], she then had the presence of mind to strip down to her nightdress, put the forensically-incriminating clothing in the washer in order to frame Jeremy, then waited while the clothes washed, then maybe put the wet clothes away somewhere to dry inconspicuously as she killed herself while dressed in her nightdress?
This is not a conclusion, however. I am neutral and I'm willing to find holes in this. Something that Jeremy does have going for him is that the pattern of the blood stains on Sheila does not seem very consistent with the idea that Jeremy shot her.