Translation:She gets dressed to go to her friends' house.
"She gets dressed for going to her friends' house" is an unnatural sentence. In particular, "for going to" is not the best translation for "pour aller" and also has an unnatural phrasing in English.
Although "pour" literally translates to "for" in English, the phrase "pour aller" means "to go to."
Also, "aller" in its infinitive form means "to go" and would never be translated as "going" in the present.
Just curious, where are you from?
Where I live there are definitely instances where "for going to" is not unnatural. Usually when asking for directions or talking about an object.
Natural Examples: What is the best road for going to Paris? This item is used for going to the beach.
Do the people where you live say: "We get in the car for going to school" or "we get in the car to go to school" ?