Ahhhh, been there, done that! And... "Student X" got to remediate (a couple times), recieved some one on one counseling in regards to her outbursts and skill performance that was filled with "make up" work that included extra pool time that consisted the remedial skills. (Pain and TIME are MY friends) My bullheaded weak-link DID "see the light" and went on to become a pretty strong diver after she discovered that I am far more stubborn than she.
Peer pressure Can be a fine thing in regard to comments like "Do you mind not doing XYZ, I'm trying to learn XYZ... Peer pressure is contagious and often effective.
As far as your Instructor being nice, he/she will continue to be nice until he/she feels it's time to cease being nice. This depends on the issue. Every instructor has their "hot buttons" which I'm sure your friend MAY soon discover. Don't let your instructor's sweet disposition fool you, Instructors don't get there with the wool over our eyes and hand holding lasts just so long. We're looking for students that are uncomfortable, scared, argumentive as such are more often the signs of stress in a student who is fighting a battle of reason over "skill X" or just plain SCARED. If I had to make a hard pressed guess, your instructor is watching this student closely and is formulating a plan to 'train" this student to overcome the issues with the skills she's hanging up on and flipping out over.
She might be really spun out over mask clears (Guessing here as I am not there), some students have real issues with nose breathing at the wrong moments and that sensation of water up the snout and freak them out in a huge way, and... once fear sets in, well... Fear feeds the imagination, even a midly scared student can and often will become very unreasonable, even down right nasty. Should the issue simply be that a tornado hasn't dropped a house on her yet and the ruby red slippers remain to be recovered, rest assured that the instructor will be addressing THAT as needed.
You have the ability to speak to her yourself about how her actions impact your experience with the class and of course, it won't hurt to encourage her.
As far as her issues in the class, I'm sure the instructor will be dealing with her very soon.