On top of Davidmil's list I'll add....

6) Poorly tuned bow/arrows/dull broadheads
7) Not matching head style to set-up
8) Poor shot SELECTION
9) Simply not reading the signs of various hits, and then not knowing how to proceed.

BigDog,
One of 2 things happened to your arrow ....first you probably hit a rib or 2 pretty hard which stopped your arrow from getting completely thru..........
Then either:
1) the movement of her near side leg pushing back against your arrow shaft as she ran broke it off
or
2) the part sticking out hit a tree or brush as she ran.
The bend was cause by a force pushing sideways on your arrow, and these are the only possible causes.
Your arrow didn't break on impact.