My heart is broken and my mind confused

I have two daughters with two different stories (as usually is the case).

One adamantly swears she did NOT push her sister, that she just wanted to get past her and might have bumped her. She has cried many tears.  She is upset that we would believe that she would hurt her sister.

The other says that her sister "lost it" and not only shoved her but had her hand back in a fist for a minute like she might punch her too.  She fell against this wood table, her arm was sore for several days and her foot has really hurt her since and is getting worse, so she went to the Dr.  Turns out she has a stress fracture.  She is broken hearted and says she feels so alone because no one believes her.  Her parents don't believe her, her boyfriend doesn't believe her.  No one believes that her sister would do such a thing.  She says SHE wouldn't believe it either, that is why she was so scared when it happened. 

WHAT IS A PARENT TO DO IN SUCH A SITUATION???  I keep saying that I will not take sides, that I was not there, no one was there to witness it and that everyone has there own sides and own perceptions. 

But Kallyn can here the hesitiation in my voice that I don't believe Karli would do such a thing.  I told her maybe I'm just in denial that my child is capable.  But she wants more.  She wants me to say I choose her and to punish Karli.

I am still waiting on my taxes.  Usually when we give our taxes to our neighbor he gives them back the same day or at least by the next day.  I took them over SATURDAY. This is WEDNESDAY.  I know, I know... this is tax season... I'm just saying this is unusual and I am in dire straights.  I am going to call him today.  The credit union is done with payments.  They now want the full amount by the end of the month.  $2450 or they are sending our mortgage on to the foreclosure department.  *sigh*   I almost don't even care anymore.  I am about out of fight.