It's obvious that your friend's parents have a substantial influence on her decision making, and for some reason, they object strongly to her relationship with you. The important question is WHY? Their influence upon her may be reasonable or not, depending on her maturity level, age, and capacity for self-governance. Consider whether any of the following may be accurate:
1) Are you in some way disliked or perceived by the parents as a poor influence? The reason could be a good one like drug use or a terrible one like race/ethnicity. Regardless, you deserve to know the real reason.
2) Are they punishing her for something, whether related to you or not (i.e., putting her on restriction, and thus the estrangement is not permanent)?
3) Do her parents forbid her from dating ANYONE until a certain age or forbid her from dating all people of a certain category? If so, this forced estrangement is not about you specifically.
4) Is there a chance she is using her parents as an excuse to reject you? Don't automatically dismiss this possibility. If she places a lot of value on being "nice" and not hurting people's feelings, then this could be it.
5) If you're talking about a same-sex love attraction, the parents could be homophobic and/or your friend may not be ready to come out.
Knowing more about why your friend's parents have supposedly done this will help you decide how to respond. Try to gain clarity by either talking to a mutual friend (assuming you cannot talk directly with your friend) or by writing a letter to your friend. It's okay to express that you miss her, but you should also express a desire to honor what makes her happy. If she is moving on, make sure she knows the door is always open and you want to remain cordial.
I hope you get the answers you need. It's my personal experience that two people who truly WANT to be together CANNOT be kept apart, regardless of what parents say. Typically, forbidding a relationship makes it all the MORE attractive! I know that from having been a teenager once and from being a parent and aunt to teens and young adults now.