>>648573281. Her plasma infusions are, simply put, borrowing someone else's immune system temporarily. This means every time she gets plasma she's getting a different immune system. She has no ability to build and strengthen any immunity, she only gets what is given to her.
2. The efficacy of a plasma infusion deteriorates over time, and her condition is to the point that she needs new plasma once a week.
When she gets plasma, it usually takes her out for the whole day because it makes her sick. The new immune system attacks whatever the old system failed to get, or whatever snuck in while the old system was weak in the latter part of the cycle.
3. Even with someone else's immune system, she's still capable of getting sick just like everyone else. And if she gets sick, it hits her a lot harder because a) a temporary infusion is not a replacement for a homegrown, lifelong immune system and b) she has had several major complications and chronic infections in the past which have permanently damaged her body and makes getting sick easier and worse.
It isn't a fix. It's a treatment.