Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh

 

I will advise that if she is as you said a good practicing Muslim and loves Islam  she should wear it as soon as possible as in that she will please her Lord Allah, be more accepted by your parents and I am sure you will be happy too.
If she is still hesitant, be patient and wait until she does but set a time table. If parents are requesting something from you especially an honorable thing like Hijab you should obey them and try to convince this girl to wear it as her choice insha Allah.

 

Almighty Allah knows best.