Shannon's father actually did leave a will which provided for his daughter, but Sabrina destroyed the will so she wouldn't have to share the money with the stepdaughter she hated.
Shannon is capable of representing Lust & Sloth. Two of the Seven Deadly Sins.
SAYID: Do you have a past in the Navy you neglected to tell me about?
SAYID: How does a woman like you learn to tie a perfect bowline knot?
SHANNON: By dating guys with sailboats?
Shannon's mother is Olivia Goodspeed,before the purge Olivia met Adam Rutherford outside of the Island and had an affair with him,her relationship with Horace was failing,so she divorced him and married Adam and gave birth to Shannon,then Adam divorced her and didn't want her to see Shannon because he found out the true intentions of the DHARMA Initiative which were bad and he didn't want Shannon to have anything to do with the DHARMA initiative.
There has been no evidence provided from the show to even remotely suggest this so this is a pure wild guess.
Shannon is really 22 because on the Pre-crash timeline it says that Sarah had her accident in 2001, which would also be the same time as Adam Rutherford's death. At Adam's wake Shannon mentions that she is 18.
Or the Walt she saw was really Walt, who may have been using his special "ability" to warn her about something.
What Walt said was "Don't press the button. Button Bad" backwards. It was certainly a Monster impersonation to lead her to her death.
Yes, Walt used his special ability and appeared to Shan. But he didn't lead her to Ana Lucía. He wanted Shannon to be quiet and not be killed.
Was killed because she was meant to be in the front section of the plane.
Could be correct because Boone and Charlie, who were also in the front of the plane when it crashed, have died as well.
The MIB possibly took Walts form (although as he was not dead unsure how)and used the visions to lead Shannon on a collision course with the Tailies where she would be killed by Ana Lucia, thus killing one of Jacobs candidates but indirectly so not breaking any of the "rules".
When the MIB takes someone's form or causes a vision of some kind, he invariably appears as someone/something extremely important to the person seeing him (as Christian to Jack/Claire, as the horse to Kate, etc.). Walt had no connection to Shannon prior to being on the Island, and their only real connection was that Shannon had agreed to take care of Vincent. Plus, Walt isn't dead, so the MIB can't appear as him.
Jacob touched her after her father's death. The Man in Black said that Jacob touched people when they were in a sensitive time of their lives.
We know that the Man in Black is somewhat telepathic, that's how he could take the form of Yemi, Christian, etc. He used that power to make Shannon see Walt.