*Note - my true assumption is the block above the last line; everything above is speculation*
She doesn't say she's taken Immuno-boosters in his room -_-
"Anti-biotics and herbal supplements that should bolster my immune system"
Bolster how, and for what purpose though?
Maybe she'd just rather not get an even WORSE reaction down the line if she attemted to weaken her immune system, it waking up to find way more bacteria than should be there, and start freaking out, it'd be all like "Ey yo Tali, sweet moves up ther-WOAH SHIT, ENEMIES EVERYWHERE!".
Or maybe by bolster, she means for the act of taking off her mask, which would actually be suppressing it. Keeping her reactions calm and under control for the time they have together.
And then the question is: is Tali fighting her reaction on the collector base? No way to tell, but all we know is later, yes, she is sick. Her system would either have been suppressed during the whole mission, or she would have been fighting it the entire time. Tough girl
I'd like to believe the meaning of the word 'bolster' is different, personally. And maybe by 'immuno-boosters' she actually means 'supressants', but doesn't want Shepard to worry about her, knowing he isn't very medically minded? OR maybe bolster is something like 'make the reactions less severe'.
And then the wild-card, Mordin Solus. How does he know about the relationship? Ken and Gabby? Or did Tali go to him herself? Maybe well working on the genophage cure, he started a side-project to assist the Quarian immune system. Maybe she volunteered to be part of the trial, I mean, this is Shepard we're talking about (I don't know about yours, but my Shepard is a sexy beast, modeled after me of course, just with better hair, I can't get that lift he has), and she does love him.
I have a feeling by 'bolster' she just meant it would make the reactions less severe. Like instead of bolstering the system to make it MORE protective with the same effectiveness, it was temporarily boosted to kill infections right away, so later there wouldn't be as many. It'd be like it added laser turrets to assist guard dogs. I bet she went to Mordin, and cooked something up. You know how Mordin loves a challenge.
Just me though. I'd do anything to defend Tali, even if I have no idea what I'm talking about. Especially medical stuff.