Probably quite small, and I think she is probably telling the truth, but the presumption of innocence is an importsant principle, and is in danger of getting lost.
I assume you mean the presumption of innocence of the alleged rapists, in this case, As NS says, she has been convicted and so the presumption of innocence doesn't apply to her.
In any case, presumption of innocence is a legal thing. It does not mean we can't form an opinion of guilt if we choose and if you think she is probably telling the truth, then, by definition, you think the Israelis are probably guilty of raping her.
My personal opinion is that technically, she was lying when she made the accusation. That doesn't mean that the police did not force a retraction under duress or that the other injustices alleged by her lawyer aren't true.
Unfortunately, there is video on some of the Israelis' phones that seems to show the sex was consensual i.e. they were filming it, so my opinion is that while the Israelis aren't strictly guilty of rape, they are utter shits and really do deserve to go to prison and the woman deserves to be treated leniently and sympathetically.