The Dolgoruky family were well known in Russia, although I have not heard of this member of it. It is intersting. The second wife of Alexander II was a Dolgoruky Princess, and the marriage was a morgantic one. What made this Princess think she would have married Alexei? Did they have a youthful crush on each other? She was three years younger than him, thus only 10 or 11 when he died.
The Dolgorucky family was a important noble family, but unless the laws regarding marriage of romanovs changed after the revolution, this marriage would have had to be morgantic. And I am sure Nicholas and Alexandra would have wanted Tsarvitch Alexei to marry
a suitable princess so his children, if any, could be full legtimate Romanovs, and thus continue the sucession. He was their only son, their only hope for the bloodline of Nicholas II to remain on the throne of Russia. They would nt have wanted a morgatic marriage. But if the laws had changed to allow marriage with members of the Russian Nobility, this Princess could have been one of the prime contenders.