Maybe your boyfriend is just 'hoping' that once she is in the rehab this may fix her. Maybe this is why he just cant say anything right now, he doesnt want to rock the boat.
Seriously though, unless it was her decision to go into rehab, chances of recovery may not be that good. Some addicts I know, will keep doing it right up to the last minute (making sure they are sober before they go in) Most have to be sober on entry. This tells me the daughter has a big addiction problem - so lets pray she gets into rehab and finds her way.