LOL...... if it was not wrong then why did "allah" send a specific commandment sanctifying this marriage ?
There would have been no need for that,
Quran 33:37 "And [remember, O Muhammad], when you said to the one on whom Allah bestowed favor and you bestowed favor, "Keep your wife and fear Allah," while you concealed within yourself that which Allah is to disclose. And you feared the people, while Allah has more right that you fear Him. So when Zayd had no longer any need for her, We married her to you in order that there not be upon the believers any discomfort concerning the wives of their adopted sons when they no longer have need of them. And ever is the command of Allah accomplished."
Funny how allah even took his Son's Name so as to avoid confusion.
BTW a cousin sister is blood related , a adopted daughter is NOT. But if you want to marry your cousins, go ahead. LOL.