As long as the dermis is not injured, it is impossible to leave scars. Dermal layer injury will leave a little scar more or less. The bigger and deeper the wound, the greater the possibility of leaving a scar.

Since your sister has been scalded and blistered, she must have hurt her dermis, so there will definitely be scars. If a single blister is large in area and high in height, 100% will leave a visible scar. If the area of a single blister is not large, but there are many small blisters connected together, it is hard to say. There will definitely be some scars, but the healing is not necessarily obvious.

But I don't think you're worried that your sister will be disfigured-since you said "the doctor can't guarantee", it means that the burn is not too serious, and it may or may not leave a scar. Even if you leave a scar, the scar tissue will not be too deep to handle. When the wound looks similar, you can go to a more reputable beauty hospital or beauty specialist. There are many ways to treat minor injuries now. Sometimes a few dermabrasion operations are enough, and nothing can be seen by rubbing the starch bottom.

So I don't think you need to worry too much. The most important thing is to pay attention to maintenance at this stage, don't burst the blisters, and avoid eating foods and drinks that may cause pigmentation, especially soy sauce!