Thanks for the query to H.C.M. Forum.
Stomach pain means pain in the epigastrium
( upper part of abdomen) ,just below thorax.
As you mentioned in your query that she vomited purplish black vomits amy be due to ,
1 Laxative poison as this developed acute hyper acidity and this causes vomiting , can be confirmed by upper endoscopy
, so consult a physician and get his opinion.
2 As you stated that there is pain in the abdomen and constipation
( not able to pass stool) and no bowel movement .
As I have seen in my so many patient that after 4-5 days of constipation they develops black color vomiting as bowel don't pass any stool .As your friend is feeling very weak so may be SUB ACUTE INTESTINAL OBSTRUCTION
, can be confirmed by a surgeon & colonoscopy
In this case please consult a physician and get his opinion then surgeon ( if necessary) , mind this is an emergency. Good luck. Dr. HET