"She does not need us."
we usually don't say “彼女は私達が要りません。” If we would say that ， we say “彼女は私達を必要としません。”
There are also other way to say we in Japanese instead of 私達 僕達/僕等（often heard in various Japanese songs） 俺達/俺等 あたし達（I use アタシ達）
I learned "は" was a topic marker and "が" was a subject marker. If "us" is the topic and "she" is the subject, why is the first one attached to the subject and the second one to the topic????
I put "wa" after "kanojo" and "ga" after "watashitachi" and it accepted it. And that way sounds better IMO.
Sometimes, if not most of the time, I've seen は used in negative phrases that would take が in the positive. Why is it 〜がありません and not 〜はありません in this case?
In English we usually say, "She doesn't need US," where "us" is the direct object. But we could also say, "As for her, WE are not needed." In the latter case "we" is the subject of the sentence, not the object. If you translate the Japanese sentence into English like that, it becomes clear why you need が instead of を. I see you are also studying Spanish. I struggled (a long time ago) with how to say "like" in Spanish. I kept wanting to say "Yo gusto los libros," (a direct translation from English) instead of the correct way of saying in Spanish, "Me gustan los libros." ("The books are pleasing to me.")
What's the difference in actual meaning between "いりません" and "いらないです"? It doesn't accept the latter, but it's what I'd been told was the normal way to say "I don't need X". My understanding is that the "ません" form can be considered a bit rude/forward (https://www.quora.com/What-is-the-difference-between-%E3%81%BE%E3%81%99-and-%E3%81%A7%E3%81%99-in-Japanese backs me up here)