Should I intervene??? Niece writing to prison inmate...PLEASE help...?

Okay, my niece has a high school friend, ex-boyfriend in prison (she's 28). She has split with boyfriend of 9 years a year ago. They have an 7 year old son. She finds out her ex is in prison and in corresponding with him. The ex is going to be incarcerated for the next 4 years. I don't know why he's behind bars, she's not opened about it and says they're just friends. She recently just went back to college. She's very intellegent when it comes to her studies and finally independent, great job and all. Should I write to the ex to tell him to back off?? I want her to finish her schooling without any distractions. What should I do?? Should I mind my own business. I'm just worried. Her father does not like the idea either. Her father found out through another family member. Now he wants me to write him and inform him on how we feel...to stop corresponding. Any suggestions please...