awwwww...I'm sorry !!!
Tell your sister to write these people ASAP - they WILL write her back - I just don't know how fast -
http://www.imom.org/
They offer financial assistance to sick pets.
and also she can try doing something at some of the bigger stores - I've seen people do it all the time here in houston - people will make up flyers and ask for small donations - people jump in & donate for sick animals all the time - I know I have & will pm you