Unfortunately there is not much you or your friend can do.
The system of being marked, disfellowshipped or disasociated are set up in a way that is impossible to fight.
When specific behaviour (having a wordly friend) is discussed as bad in a talk. Any JW who knows a JW displays that behaviour, will stop socializing with them until they stop their bad behaviour. They will still talk to them in the kingdom hall tho, but preferably just to encourage them to give up their bad behaviour.
When disfellowshipped or disasociated, a announcement is made: "X is no longer one of Jehovah's Witnesses". Now all good JWs will never talk to X again unless they repent and are offficially reinstated, or when X is a close relative and important family matters come up.
As you can see, being marked means less socializing from JW.
To fight this, your friend should either give up their wordly friend and be 'unmarked' (so JW blackmailing worked) or try to convince selected JW friends to ignore her being marked, and still socialize with her.
Or she could recognize this really is a controlling cult that doesn't let her make her own decisions, and walk away.
I recommend her the last option.
As a real friend, stay with her, she needs it. Ask her who show real friendship: the JW friends that ignore her when they are told to do so? Or wordly friends that are friends regardless of her personal choices? Who shows greater love?
No need to pressure her into answering. The idea is to make her think. Really think.
Btw I assume she is marked for having a wordly boyfriend, not just a friend?