Question How am I supposed to understand this NO VERB + SUBJECT ?「一緒に！？　だと……そ、そんなことが」

I met this difficult sentence while the writer keep omits subject or verb in his writing, i don't understand at all !!. Hope some native or experts >N1 in Japanese could translate/ explain its meaning in English / rewrite full sentence in standard Japanese so i can understand better !

-Story: 3 female generals 星,愛紗,桃香さま are serving a Master (protagonist), 星 and愛紗 are subordinates of 桃香さま. One day after a conversation, 星 realized 愛紗 also like the protagonist/ the Master like her superior 桃香さま, but doesn't think Master love her. So 星 encouraged 愛紗 to love Master together with 桃香さま

星「桃香さまが主に愛されているからといって、お主が愛されぬ理由にはならぬと……私は最初から言っておるではないか」
愛紗「……意味がわからぬ」
星「石頭め。要は、桃香さまと一緒に愛して頂けということだ」
愛紗「一緒に！？ だと……そ、そんなことが」
星「一身に寵愛を得なければ満足出来ぬか？それもまた女の性、否定はせぬが」
愛紗「そのようなことは言っていない！ 私はただ……」

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Konnichiwa zeroh4nter-san!

"一緒に！？ だと……"
To...gether!?

Originally, it was a word "一緒にだと!?". It's translated "Together!?" simply.

But 愛紗 was very surprised, and she was at a loss for words in the middle of a conversation "一緒に！？ だと……".

And I translated "To...gether!?".

But I don't know if being at a loss for words expresses surprise in an English-speaking society.


"そ、そんなことが"
That...Is that...

This sentence is cut off midway. The original text should continue as follows:

"そ、そんなことができるのか？"
Is that possible?

or

"そ、そんなことが許されるのか？"
Is that really allowed?

Her loss of words in the middle of the conversation shows her surprise.

I'm not sure how to express these Japanese expressions of surprise in English.


NANGI