Sharon can do it if she wins round 1 or 2 in the F3 HOH. Adam and Ryan are morons of the highest degree, and the round 3 HOH is always intellectual, so if Sharon wins round 1 or 2 she will wipe the floor with them.
She is guaranteed 3 votes at least. I very much doubt the likes of James, Chelsia, and Josh care about whether they look bitter or not - everything they've done inside the house has made them look like nasty, bitter people and everything we've heard them say in the jury house has been bitter. James was even bitter to the girl he apparently "loves" and blamed her for his own eviction and reduced her to tears because of it. These 3 people are not fair, and they are bitter, and don't care if they look bitter, so they will vote for their last remaining team-mate Sharon no matter what.
Natalie will be pissed off at her boys for betraying her, there's a chance she could vote for Sharon in the final. She voted James back into the house just because Josh told her to, so she could be just as easily convinced in the jury vote by Josh or James or Chelsia.
I think Sheila likes Sharon more than Ryan. Ryan took that money away from Sheila as well, and I think Sheila won't have forgotten that. There's no way Ryan would get her vote. As for Adam, if he does vote Sheila out then it is the ultimate betrayal, even worse than him betraying Natalie, because Sheila genuinely wanted to take Adam to the final and she thought he did too, and she thought they had a great relationship. She will be furious that Adam ultimately chose Ryan over her.
Matt is the only juror who I'm sure would vote for Ryan or Adam. But then again, he'll be in the jury house with Natalie and Sheila, both of whom he gets on well with, both of whom might sway him into voting for Sharon if they themselves hold a grudge against Ryan or Adam. So I wouldn't completely write Sharon out of this game yet.