Good questions all. I will try and answer them based on what I know
1. Unknown. My gut reaction is that since you are undead, you aren't dead so your time spent as a vampire wouldn't count for the purpose of resurrection madness.
2. Expect table variation. I think the easiest approach (and one very in keeping with Ravenloft), is to have her alive and well despite her apparent death. Perhaps the Mists raised her as well, or perhaps there are other sinister forces at work. I would play it up completely and have her very unhappy to see her murderers. Rather than rolling randomly on the table, as a DM I would instead choose the most sinister and twisted options (such as flayed skin) in order to "punish" the PCs.
Failing that, it could be another hag either masquarading as Jenny Greenteeth, or perhaps going by another name but serving the same roll (perhaps her sister?)
3. The factions really aren't present in Barovia outside of those few members who were present in the Quivering Forest when it was sucked into Barovia (Orasnou is situated in the north-eastern corner of the Barovian map, with the Quivering Forest north of Orasnou off the map).
The lack of a true faction presence means that Faction charity is not available in Barovia. Instead, characters wishing to be raised need to either seek out Jenny Greenteeth, be revived by a fellow PC, or be raised by the Dark Powers. Other options may be available in some adventures although they too would likely have terms and conditions attached to them. Nothing in Ravenloft is free. Everything comes at a price - and gold is rarely the only cost
Faction Charity still exists for those characters who are not trapped within Barovia however.