coworker tried to embarrass me in front of another

I work at a private practice cardiologist. i am f25, most of the other girls I work with range from 21-28. the one i am speaking about is on the lower end. most of them are very normal and nice. except this one. let's call her and her sidekick...thing 1 and thing 2.

I am about to start to room a patient. my boss, the leading cardiologist, sees me and asks "are you putting in patients?" I said, "i was just about to room one right now." the rest of the conversation goes: "well, I need someone to sit at checkout and help the front desk. it gets so busy." "if you want me to sit there i definitely can." "yeah, move your stuff over here and help the girls in the front. don't let it get too busy up there." "sure thing."

a few minutes later, thing 2 walks by and says "oh, I guess i'm the only one doing Dr. so and so's patients. great." thing 1 isn't far behind. i say, "oh, i'm sorry. Dr. (boss guy) said to sit here." thing 1 pipes up. "yeah. he got angry you were sitting in the back and told you to sit there." i didn't know exactly what to say in the moment but wanted to make it clear I wasn't feeding into it so i just sort of laughed and said "okay" because a.) she wasn't even there to be privy to such information and, b.) that was not true.

it just obviously bothered me even though I didn't make it known in the moment. this girl is not the most mature or nice person i've ever known. needlessly catty is how i'd describe her. high school mean girl type. she decides how she feels about you, will gossip about you behind your back, ice you out for no reason, and make unnecessary comments such as that. and before you say "go to your boss/manager" that will not work. trust me. the boss is lazy. the manager likes her. I just don't understand why she has singled me out/decided to be passive aggressive towards me.

all I do is my job. albeit, it entails slightly different duties than hers at times and perhaps it looks like "i'm not doing enough" to her. but, nevertheless - I do my job. the boss never has any issues with me. no one else has any issues with me that I know of. I treat everyone the same.