Unpredictable aggressive behaviors

So little rue is a chihuahua mix that I've adopted 2 1/2 weeks ago. Let's start off saying the good things about her, she's very intelligent and has mastered come, sit, and stay in this time. She's also working on focus (which is looking me in the eye for an extended period of time). She has learned to walk on a loose leash and to follow which ever direction I'm heading when I say come on. All amazing and on top of it all she likes to just curl up on the bed or my lap while I'm working.

There's just one big but, she has this aggressive tendency that's somewhat unpredictable. In the beginning, she would lightly growl when someone would pass my room. Over time, it's escalated to the point of lunging at my bedroom door with her hackles raised and barking like crazy. While it was at the point of just low growls and barks, I thought I could handle it and nip the behavior in the bud, but so far she's directly lunged at my roommates 4-5 times before she started to get locked in my room. She knows my roommates and will follow them around when she meets them in the living room, but when they pass my room or enter the apartment, she's spazzed out about them. She's also very aggressive to newcomers and randomly barks and growls at people on walks(randomly since it only happens 30% of the time with no pattern of who she's barking at).

Now this may seem pretty predictable, but she's varies in her response constantly. For example for the past 3 days she had been getting progressively worse, and I naively thought I could still safely keep the door open. Well, I was training focus with her in the living room and she's been doing really well. My roommate passed us to go to the bathroom and I bring her back to my room(across from the bathroom) and continue training. My roommate comes out of the bathroom and rue is looking right at me then without a growl or bark she lunged directly at my roomie. It scared the crap out of both of us. It seems to be territorial but she's ok with people passing the room when she's not there so it's a little weird. After this big response, she's had a full day of only lightly growling at people and then just light warning barks. I thought, "wow, this dog was just settling in perhaps it'll settle down now." It was like the aggression was all gone. About 20 Minutes ago, though, she fully lunged at the door again and she was harder to recall.

Honestly, I'm at my wits end with this dog. I maintain a strict schedule of daily walks (live in an apartment so she has to be walked to go to the bathroom) and scheduled eating. She doesn't get to eat or go through doors without sitting. She definitely follows "nothing in life is free." I also have tried reducing as much stimulation as possible, but I can't stop people constantly coming in and out of the apartment or people passing my room. I've also tried a little bit of counter-conditioning. But there's no real reduction or even stabilization of her aggressive behaviors. She's very hyper vigilant and reactive.

So here's my situation. I adopted her as an assistance dog for social anxiety and panic attacks. I live in an apartment building on a school campus. I adore all the great personality traits mentioned above, but these aggressive tendencies are unacceptable. During the summer, I go home to a household that's very loud, has tons of visitors and two other dogs. I have to go through the airport at least 4 times a year. And I can't have an animal that's aggressive on campus. Realistically, how likely is it that I can modify these behaviors and how much of a time commitment would it take? I'm a full time student so I can dedicate enough time to take care of her and do regular training each day but I can't have a constant commitment realistically and do school and take care of myself. I can still return her to the rescue where she will be guarenteed a foster home until she's adopted again. Would it be best to cut my losses and return her or would it be realistic, with a reduced budget that can't afford a lot of professional training and the qualifications she must fit into to keep her?

Go back to rescue and ask if she was like this there and what background were they given when they took her in. If you explain to them they should help you.

I talked to the rescue and she has no known background but the foster mom told me after the fact that she did seem to be hyper vigilant while she was at her house and barked more than other dogs. It's a bit upsetting that she failed to express this personality trait since I've had a hyper vigilant dog before(not aggressive since she was well socialized as a puppy) but I know that over stimulating environments can be too exciting for these dogs. The best advice I got was to use happy traveler for her, but I feel like that's just a stop gap solution since it doesn't really change the behavior in any lasting way. At this point, she's generally not allowed outside my room since she's started lunging at my roommates and growling at them in the regular living area. I'm starting to believe it may be better for her to be given a more suitable home than what I can offer.