That… is an anime gag.
There are medical conditions which can cause this, but if there’s breathing issues then that’s a clothing issue and if the armor is causing you to be short of breath then… the armor is useless and not doing its job.
Corsets and any sort of binding that doesn’t allow the lungs/chest cavity/ribs/diaphragm to expand will cause shortness of breath in… either gender. It is historically more common in women because of, well, fashion. You didn’t need to be well-endowed to fall prey to the whale-bone corsets of the 18th century. (Which also led to miscarriages.)
The argument you’re referring to is one common among fanboys, primarily as a justification for boobplate and the fetishistic armor choices for female superheroes. For all it’s claims to realism, it has zero bearing on reality.
The weight of your boobs doesn’t make you short of breath or hamper your ability to breathe. It can, in some cases, be painful during high energy activities when they’re bouncing around but the solution is called a sports bra. (Besides, big boobs can disappear fast depending on the type of activity. You ever seen runners or professional female athletes in almost… well, anything? Muscle burns fat, and your chest muscles will start with your chest. No fat, they shrink.)
The Most Common Superpower joke is that women get to keep theirs and stay conventionally attractive when engaging in highly aerobic activity.
If we want to start with the issue in the presentation of female action heroes it begins here. (And that men, and some women, usually don’t understand how breasts work.) Or have this idea the issue has never been addressed because women don’t participate in sport activity anyway.
Breasts. Are. Just. There.
She’s a superhero. Her armor is custom designed. If whoever made her armor didn’t take into account the size of her chest or provide support then they are crappy at their job and armor design in general.
The issues we run into with armor is when it is either:
A) Not yours. Or..
B) One size fits all, but you’d still be able to function in it.
If you can’t move in the armor then that’s an issue that needs to be addressed at a design level but it’s not insurmountable. This is why armorers and tailors exist.
Besides, if the other option you’re considering is boob plate then that wouldn’t solve the issue. I guarantee boob plate is more uncomfortable, and will guide weapon points straight to your heart. This is an argument I’ve seen brought up a lot (by men) to justify the existence of boobplate or going without armor for “realism”. It is not only BS, it’s annoying. It ignores both reality (female combatants of history) and human ingenuity to prop up outdated sexism. It’s like they think female athletes never address the issues of their chest size. Well, I’m here to tell you: we already solved this one and it’s called a sports bra. In the real world, we get a bras that are designed to support the weight of our boobage during athletic activities.
Women can, however, STILL RUN without problems with a regular bra or even no support at all.
You, however, may want to address the underlying sexism nipping at your approach to this character. If you genuinely believe cramming big breasts into a tactical vest is going to cause breathing issues then you’ve got a lot of your own to work out. That is also the problem with sexism. The misinformation is so baked into every bit of common knowledge meant to justify a certain sexist approach then held up as realistic that most people never think about it.
Again, the kind of breathing issues we’re talking about come from corsets and not armor. A corset tightens your waist, and will result in issues because of the diaphram/stomach can’t expand. When performing aerobic exercise, you need your diaphragm (thus expanding your ribs) to breathe. The diaphragm allows more air to pass through your body, which means more oxygen in your blood being carried to your muscles. Without them, you’re stuck breathing entirely with your upper chest, and that will be a problem when engaging in athletic activity. If the expansion of the chest is also cut off, then… you’re really up a creek. This is what causes the fainting fits of the 18th century. Women wearing clothing that doesn’t allow them to draw enough oxygen into their bodies to keep their brains cognizant.
It’s also why you never want to bind your breasts with anything like Ace bandages because Ace bandages are designed to continually constrict around an injury and create pressure to halt the blood flow. They can tighten so much that they crack the breastbone or the ribcage, and that is what causes shortness of breath rather than the breasts themselves being bound.
You don’t get this problem if you bind with just cloth, but it’s also shit for support.
Breathing issues are a problem for men when they wear clothing styles that ensure their diaphragms can’t expand or just don’t breathe with their diaphragm when fighting.
If her armor causing shortness of breath then that’s not armor, it’s fetish gear. It may be great for a bondage session but it’s not meant to be worn combat. (And if what she’s wearing is causing shortness of breath anyway, then she just needs to stop wearing it. That’s still the fault of her clothing and not her breasts.)
Besides, a woman with large breasts would have issues finding bras that fit her anyway and would probably be specially ordering them. Most malls and sports stores have bras for A, B, C, and some D but not a lot. DD’s can have trouble finding comfortable breastwear, especially ones in the six foot range.