I would give it to Nandini if at this point she still holds firm on her ground & refuse to let Kunal back in her life for the very same reason she broke up with Kunal last week. For me, that will be Nandini's demonstration of friendship.
If Nandini is right on her part about her concern & friendship for Mauli, then she herself should not be dating Kunal anymore in the first place now. Let Kunal take a decision that he wants to live with Nandini & let Nandini take a decision that she doesn't want to live with Kunal at this point if friendship is so sacred for her.
Rule of friendship- Never date your best friend's ex. I repeat NEVER. (It is breaking the code of friendship where it is mutually taken that one who wronged my best friend wronged me as well). This is a code even practiced in supposed developed countries of the world.
This is the first time Nandini tried to think about Mauli, but even here she left Kunal hanging in between without proper closure. She kept quiet when Mauli was molested & tried to tell him his reality. She kept quiet when Mauli was again manhandled & mistreated by Rajdeep countless times. She kept quiet when Kunal began his advances & rather then letting Mauli know about that she accepted his proposal.
It was Nandini who broke the friendship code by never choosing Mauli over her interest in Rajdeep & Kunal. Mauli still pushed her way to get her out of her damsel & get her back on her feet. Kunal could have never done that if it was not for Mauli's constant consideration for Nandini. It was Nandini's decision to get married to Rajdeep despite Mauli's warning & stay in that marriage until she saw Mauli as a hope to hold on to.
Mauli healed her & made her again, Nandini broke her by not turning down Kunal's advances & warning Mauli about him.
So, NO, Nandini is not a better friend than Mauli in any way.
And no, Nandini wasn't ready to die for Mauli out of sacrifice but because she was in that situation where she could see no escape. She was abducted & put in that life-threatening situation where she did not see any exit despite her attempts.She did not willingly walk into fire to die.
If Kunal isn't Mauli's to hold on to, then he isn't Nandini's too to give back to Mauli. She lost this battle & her ground the day she said YES to Kunal without blinking. She lost it on the day when they had sex without any introspection of their deed.
Moreover, Mauli should be thinking about well-being of Nandini every time even when she has been broken so much (and if she doesn't then she is the horrible person) but it's fine if Nandini doesn't think about Mauli at all, all the time but does this one task of going away from Kunal for the pinky promise (since she has suffered so much in past) & yet, she is a better friend. WOW!!!! All hails to you.
If Mauli is a horrible friend, then Nandini is more horrible than her as a friend.
But of course it's useless to talk about it to someone who has dictated a verdict already that Mauli has always been wrong.