"для вашей подруги и ее коллег"
Here is a compound sentence. Second clause (which we need) is: "для _______ подруги и ______коллег это совсем нормально" (for ... it is quite normal). Here subject is "это". The girlfriend here is not a girlfriend of "это" and the colleagues are not colleagues of "это" so "свой" is inacceptable in all cases. "Свой" can be related to the subject of the same clause only.
To detect structure of the sentence you can remove word by word: select which word can be removed without removing others and the last word remained is a subject. It is quite an intuitive way but it helps me.
для вашей подруги и ее коллег это совсем нормально =>
для подруги и коллег это нормально =>
для подруги это нормально =>
это нормально =>
это
for your friend and her colleagues it is quite normal =>
for friend and colleagues it is normal =>
for friend it is normal =>
it is normal =>
it is =>
it