I agree with your summation that it is not a werewolf.
The single werewolf taking down vamps quicker than vamps can drop a werewolf is kind of an urban legend. Yes they are physical nightmares, but so are vampires. The lower gen vampires are virtually incapable of losing to an Elder Garou Ahroun (warrior types of the warrior race of Luna) Situational circumstances mean a lot. Clan of the vampire means a lot. Generation means more, and age means a good amount. (the actual accrual rate of experience points for elder vamps is something I always disagreed with and we had house rules in my circle's games.)
Anyway, if you run the situation above with an Ahroun and Sharon was caught flat footed, then she is lucky to be alive.
I think it was another vamp
1-Astrid female for my friend
Ayhsel but a Tzimisce shape shifted into their combat form, with a touch of celerity can fill the bull.
2-Enid. Wolf Boy/gangrel serving the princep and more importantly Publius...end result desired, to cause Sharon to fail not kill her.
3 Virgil/Publius for his own reasons. A hyped up super bear could hit and run. A light scratch from his claws (if he is who I think he is) would be enough to debilitate Sharon with pain.
4- someone sent by Vision Girl Inanna (Artemis for those resisting change) to test her boy out but Sharon happened to walk up to too soon so rather than blow his cover he shift, hit her and left her.
About a dozen other weird thoughts... really more like 5 but yeah let's go with it.
Peace