What would you do? (budgie question)

One of my birds was diagnosed with avian gastric yeast today.

So, I recently added a second bird, and like a dodo I didn't get her well-bird exam scheduled until after her quarantine period. (I know, I know....believe me I'm beating myself up over this now. :( ) I introduced Iris and Ivy (who went through quarantine beautifully, is endlessly active and playful, and just a joy to behold) and THEN brought her in for her well-bird.

Her fecal showed a VERY small number of AGY, and my vet gave me a HUGE amount of information to sort through. I wish I had taken notes, it was a lot to take in!! Here's what I'm remembering, please correct me if any of this is wrong:

-It's almost impossible(maybe totally impossible) to get rid of it entirely.
-Aggressive treatment NOW (while she's still a baby) MIGHT get rid of it, but the treatment is going to be stressful for her, and the stress of trying to treat her could potentially bring on a flare-up.
-The medication involved in said aggressive treatment could also have long-term harmful effects on her liver and other organs.
-NOT treating could lead to clinical illness, or she might be an asymptomatic carrier forever.

My vet is a very experienced avian vet who owns a bird-only hospital. Had she said "I think you should do X" I would do what she advised without hesitating. However, she gave me options and said that there is no wrong answer in this situation.

-I can separate the birds and treat one or both of them.
-I can wait and bring back another fecal later, as well as monitoring Ivy's weight and condition.

Since Ivy is (in the vet's words) "fat and happy"...plays all day, eats vigorously, has normal poops and no signs of illness, I'm tempted to take option 2. I have a gram scale I can use to weigh her, and I can certainly bring in a fecal sample to the vet any time she so much as has a feather out of place. (the birds live at my work, and I can see the vet's office from the front door!)

Then again, I don't want to leave a potentially life-threatening disease untreated only to find out too late that I should have done something. I know how well they can hide signs of illness, what if one of them has a flare-up and I don't catch it in time? The vet did say that her airway was a little irritated, but she didn't seem too concerned, and she said it was likely due to the fact that she needs to bathe more, her throat swab came back quite dusty.

What should I do?

I would separate the birds, and watch them both carefully, and bring in fecal matter for a test for each bird in whateer period of time the vet thinks would be wise.