Is it permissible to supplicate for one's deceased female cousin to be a bride in Paradise, or is that considered an transgression in supplication?

It is permissible to supplicate that this girl be your wife in Paradise, but what is better and more beneficial is to supplicate for her mercy, forgiveness, and elevation of rank in Paradise. One must be wary of excessive attachment to her, as she is a stranger to you, and be content with Allah's decree and destiny. Calamities are a test that distinguishes the truthful from the distraught, and the patient are those who attain the great glad tidings and abundant reward. Remember the words of Allah Almighty: (And We will surely test you with something of fear and hunger and a loss of wealth and lives and fruits, but give good tidings to the patient Who, when disaster strikes them, say, "Indeed we belong to Allah, and indeed to Him we will return." Those are the ones upon whom are blessings from their Lord and mercy. And it is those who are the [rightly] guided.) [Al-Baqarah: 155-157]. It is also appropriate to supplicate with what is mentioned in the noble Hadith: "O Allah, reward me in my calamity and replace it with something better."