Dione Melville fell ill at the property in East Calder and police are now investigating whether drugs were involved.
An ambulance was called to the house but Dione died shortly afterwards.
Two other girls, both aged 15, were taken to hospital at around 9.50am.
A Police Scotland spokeswoman said: “Police in West Lothian were called to an address in the East Calder area at around 9.50am on Sunday March 27 following a report of concern from a teenager.
“The Scottish Ambulance Service attended and a 15-year-old girl was sadly pronounced dead a short time later.
“Two girls, also aged 15, were taken to St John’s Hospital as a precaution.
“The death is currently being treated as unexplained.
“A report has been submitted to the Procurator Fiscal and inquiries are continuing.”
Lisa Grubb, West Calder High School acting head teacher, said: “Dione was a popular girl and this is clearly a very upsetting time for her friends and family.
“Dione was an ambitious young lady who had plans to work in hairdressing and in the beauty industry after leaving school in the summer. She was very focused on her future and the thoughts of the entire school community are with Dione’s family and friends at this incredibly sad time.”