BM potty training

My granddaughter just turned 3.  She has been potty trained for aabout 2 months and refuses to use the toilet when she needs to have a BM.  She will hide behind anything, come out from where she just defecated and have a sad look on her face.  She only wears panties during the day and will use the toilet at home.
I must tell you though, that we recently received custody of our grandchildren, she was living with us at the court ordered time, her mother recently moved out, she doesn't see much of her father, and I had surgery one week ago.
I know that all of this is a lot for a 3 year old, but this was happening before the surgery.  

Any suggestions?  I used to provide childcare in my home and never came across this situation.  HELP!!!!