Thank you for your warm welcome.
Yes, the difficult point is how to ensure her return. She has no job, and doesn't go to school either. Only possibility would be a fact that she is a single mother and has a baby in philippines. Her parents passed away and she lives with her grandparents, and also has several younger sisters who needs care.
In such a case, would birth (and death) certificates of her families help her visa?
My immigration status is what I haven't considered before. I came here with Tier2 visa as an internal transfer of Japanese company. Valid period is three years.