Questions & Answers about Если рана маленькая, её заклеивают пластырем.
Because маленькая has to agree with рана.
- рана is feminine, singular, nominative
- the adjective маленький changes to match it
- so маленький → маленькая
This is normal Russian adjective agreement: adjectives match the noun in gender, number, and case.
Because её is the form used for a direct object here.
- она = she/it as the subject
- её = her/it as the object
In this sentence, the wound is not doing the action; the wound is the thing being covered. So Russian uses её.
Compare:
- Она маленькая. = It is small.
- Её заклеивают пластырем. = They cover it with a plaster.