Too much to really address here (although I don't agree with most of it) but the suicide theory is not at all "fantastical". Her thumb was still firmly pressing the trigger of the gun in it's most rearward position. That in itself makes suicide very likely, if not the most likely explanation for her death.
If her arms were "tucked under" her then how did the gun end up in the position and state which it did? It would have had to be transferred from the shooter's hand to hers all the while whilst holding the trigger fully rearward. That would be a very neat trick for anyone to accomplish.
Just for clarity on this aspect, but for me there is zero possibility of suicide in this case, I didn't say her arms were tucked underneath her. Simply that the shooter sat astride her, effectively pinning her whole body down, arms down, and creating a point blank injury. But also same position would mean her hands didn't get blood spatter. There is no evidence her hands were in a position to have made the shot and there is zero evidence that she did. In fact, even the very negligible evidence proves that she absolutely didn't.