Hello Italian and welcome to the group
It's good to hear that your D37 is open to meaningful treatment. My suspicion is that effectiveness is less about the age of the pwBPD (person with BPD), and more about the person's willingness to do the hard work to change.
Are you in the USA? One place to start would be contacting
McLean Hospital in Massachusetts; they have a BPD-specific program and it's considered to be a reputable, cutting-edge treatment center. Even if for some reason it ends up not being a good fit, you could ask if they have info about or refer to other trustworthy programs.
If your D37 is currently in outpatient treatment, you can ask her current providers for referrals, too. I'm assuming you are able to be involved with her care (i.e. has she signed disclosure/HIPAA forms)?