The hospital is insane.....your sisters milk should come in soon...there is no reason for them to push Reglan on her now!
I have been/am working my ass off to get my milk supply back up after a severe case of mastitis on day 9 post birth (check my other posts for the insane story)--- it's now day 23, and we are able to supplement only with breast milk, and most of his food he is getting directy from my breasts...
I say this because even I, with all the major issues, would not consider Reglan because of the side effects. I did order some Dom, but its not hear yet...hopefully I will barely need it when it shows up

So, its waaaaaaaaaaay too early for them to be pushing that stuff on your sister!!!! Her body is healing from the rough labor and section--and is probably just a little shower with getting her transition from col. to milk....but certainly NOT abnormal at this point!!!
Good luck to her! I am sure it will all work out quite well....with a little time...