珠世さんに手当をしてもらっているが、怪我は完治してない
Why is the progressive used here?
珠世さんに手当をしてもらっているが、怪我は完治してない
Why is the progressive used here?
Assuming Tamayo is not present in this scene, this ている is not progressive but perfective. It describes the continuation of a resultant state. See: When is Vている the continuation of action and when is it the continuation of state?
珠世さんに手当をしてもらっているが、怪我は完治してない。
Tamayo has treated me, but my injury has not been fully healed.
(Or more literally...) I have received from Tamayo a favor of treating me, but my injury has not been fully healed.
As Chocolate suggested, if you can understand 完治してない, this もらっている has exactly the same type of ている.
In this case, a simple past form (-た) and a present perfect form (-ている) both make sense. It's also natural to say 珠世さんに手当をしてもらったが ("Tamayo treated me, but...").
EDIT: I should have mentioned another possible interpretation. If she currently treats him on a regular basis (e.g., every week), this ている can be interpreted as "habitual aspect". See this: Habitual aspect
Therefore, if there is no context, there are three possible interpretations of 珠世さんに手当をしてもらっている:
It's progressive in the sense you have been receiv-ing treatment.
Just like in English language, it's present perfect. The action is still on-going if you will.
In your example you do not expect to have your injury heal anytime soon and the healing of Mr. Tamayo is one event in the continuation of that story.
Now if you are new to Japanese language you have to prepare yourself to see the extensive use of present of any form to express either something that happened in the past or an expected thing happen-ing in the future.