I had an issue come up recently, and wanted to get a different perspective on what to do about it. So I thought I'd ask here

Apologies for the wall of text. TL;DR below.
So I have this friend (R), whom I met through my best friend/roommate/business partner (N). Now, R has always seemed a little standoffish toward me, and has once or twice made comments (largely in ignorance) that most trans women would probably ruffle their feathers at a little bit. But I'm beta as ->-bleeped-<- and absolutely abhor confrontations, and so it's easier to just assume she doesn't mean to be rude or what not, or I'll make a point to correct her later in a way that she won't take offense at. But I've always kinda had the feeling that she was only pretending to be my friend because N is also her best friend, and we're kinda like a package deal since we live together. But we've been friends for well over a year now, and she comes to our house at least once a week, and we've been through a lot together, so the three of us are pretty much the epicenter of my little social circle.
So a few weeks ago R is graduating and throwing a party at her mothers place. I arrived a few hours before N, and I didn't really know anyone else there, so I sit down to play wallflower for a bit since R was busy with other guests. Soon she comes up and she has a friend with her whom I've only met once before and don't know very well at all. I don't even remember her name. So we started chit-chatting, and I mentioned to R about how I was getting stuff ready for my trip out to Thailand (yay SRS!). All of a sudden R leans in to the other girl and says in a conspiratorial whisper that's easily loud enough for me to hear since I'm standing right there, "She's the one that's going to thailand for the surgery" and indicates to her crotch. The other girl nods and gives an "Oh!" sounding whisper, and then they both turn back to me and get all smiley, and I'm like WTF! I don't know this person and you're giving them all kinds of personal details without asking me! In front of my face! Like I'm not even here?! At least, that's what happened in my head. But I'm Mrs. Super Spineless Beta who can't rock the boat to save her life, and so I pretend like I didn't notice how incredibly rude they were, and once again decided to chalk it up to ignorance on R's part, and figured it would be better to just let it slide and that in the grand scheme of things it's not really that big a deal, and eventually I'll get over it.
So soon after N shows up and we party for a bit, and then we decide to head over to R's new place. So it's three of us + R's adopted sister of sorts + the friend who is now in the know whose name I can't remember + N and R's SO's. We're in the living room chatting, and the subject once again turns to trans issues, this time about one of the women that both N and I work with. So N is telling everyone about how she's currently over in Thailand getting her FFS done, and she can't wait to see her when she gets back. And then R asks her, "But she's still a man though, right?". So inside I sigh and facepalm and think to myself in the most condescending tone I can imagine "no, she's not a man. She's not there for SRS if that' what you meant to ask. But she hasn't been a man for quite a while now" And I am 100% fully expecting this or something similar to come from N. See, N is my best friend for a reason. She's been more supportive then anyone else I've ever met, is incredibly well educated on trans issues for someone who isn't trans herself, and she's even helping me out with my surgery. Which is why I'm absolutely stunned when I hear her say "yes, she's only getting her face done." Again - WTF!? So...what does that make me then?
Now, I don't think N really meant that when she said it. I honestly believe that she knew what R meant by it and was speaking to that in her response without really thinking about what she was really saying by doing so. I think if I were to point this out to her she'd feel sooooo unbelievably bad about it. I can forgive her because I know her heart truly is in the right place. But R overplayed her hand. It's obvious that this is exactly how she really feels about trans women. That we're nothing more then men playing dress up.
At the time that it happened I was too shocked to say anything myself, and besides - who would anyone in that room listen to anyway? Their close friend whose hosting us whom they've known for years, or the really defensive trans woman they just met recently? The odds were not in my favor that night. I felt really outnumbered and alone.
I had hoped that over time it would just fade away and I would forget about it. Except I can't. Every time I see R now I get really uncomfortable. I just can't trust her anymore. But at the same time, it's not like she's just gonna go away. Her and N are too close, and like I said, she's been coming over to our house at least once a week. And it's been a while since the night in question anyway. Other then this one thing, we've never had an issue, and I hate to cause drama. But I really shouldn't have to feel so uncomfortable around my friends like this. It really sucks.
Should I confront R directly? I kinda feel like I should talk to N about it, and make sure that she's got my back if it ever comes up again, but I also don't wanna hurt her feelings if she really didn't mean it the way it came out. Or should I be more upset at her for the way she answered? Or am I really just making a mountain out of a mole hill?
So, if you were me, what would you do?
TL;DR - Had a close friend out me to strangers and be really rude and disrespectful to me in a passive agressive manner. Best friend didn't correct her, and instead (to my surprise) went with it. Not sure how to respond cause I'm overly non-confrontational.