Well if I find her area right, she is in a fair coverage area, with the new NV equipment, which all towers around her have, should preform better than that. If she's sure her wi-fi calling is off, then call Sprint and make sure you get a ticket number so you make sure they have reported the issue and you can follow up.
Also she have signal check installed so you can see if she's on 1x800 or 1x1900??
Rickie