She's too concerned about protecting Madoka, to the point that she is actually willing to kill Sayaka to spare Madoka the anguish of seeing one of her best friends transformed into a Witch. This is something that Madoka would never do, considering how much she value her friendship with Sayaka, and would be very OOC of what we have seen of her so far, if she would go to such lengths just to protect herself (we are looking at a girl who is willing to accompany a friend on her Witch-hunts despite the dangers which she is all too aware of).
Also, this theory may also answer Homerun-chan's actions throughout the series so far, like how she seemed hurt when Madoka called her Akemi-san in episode 1, and why she knows that Charlotte is not something Mami could handle (and how she herself was able to take down the same witch without too much a hassle. Because she herself had witnessed the Witch's ability previously). It also explains her driving obsession to prevent Madoka from becoming a MG; simply because Madoka paid a price too high to turn her back from a Witch! To Sayaka, this would be unacceptable, especially after her harsh words to Madoka this episode, she would be heartbroken if her best friend was still willing to sacrifice herself just for her sake. Just because she, Madoka, was a person too kind, a friend too good to be true.
Even if Kyubey is lying about Madoka being able to save Sayaka after she becomes a MG, it may be still possible for him to reverse the Witch-MG transformation if Madoka
wishes it so. In other words, the foundation of Homerun-chan=Sayaka theory lies in the event that Madoka wishes Sayaka out of her Witch state and succeeds in doing so (regardless his intentions and plans, Kyubey apparently honors his part of granting the wish of the potential MG).
I'm afraid my post may not be as well laid-out as I wish it so (since I'm running late for work and has little time to organise my thoughts. Alas for the parts which I have no time now to write out!
![Heh](https://cdn-forums.animesuki.com/images/as.global/smilies/heh.gif)
). So I apologise if what is written now seems full of holes (if the theory itself is not so in the first place
![Uhoh](https://cdn-forums.animesuki.com/images/as.global/smilies/uhoh.gif)
. And yes, I do recognise that a very big hole here is why Homerun-chan didn't stop Madoka from throwing Sayaka from the bridge in the first place
![Heh](https://cdn-forums.animesuki.com/images/as.global/smilies/heh.gif)
)