I do think this is the correct person. The McDaniels female that married John Harriman and lived in Oxford County Maine was Syrena C./Corinne S. McDaniels. Per research of family historian Berk Henley (who lived in Norway ME for many years, which is not too far from Fryeburg and Lovell Maine) John and Syrena (McDaniels) Harriman were married 4 Jul 1875 [you had 1 Jul 1875] in Lovell ME (source: Lovelll ME VR) and she was, according to her death record (filed as Corinne S. Harriman, Maine State Archives) the daughter of Dean McDaniels and his first wife, Mary Whitney. Corinne S./Serena (McDaniels) Harriman died 2 Sep 1923 in Fryeburg ME, apparently living her whole life in Oxford County Maine. Her father, Dean McDaniels, lived in Lovell ME for many years, which is why Syrena would have been married in Lovell Maine. I am unsure where you found her as the daughter of David/Dana McDaniels of Lincoln County Maine, which is not near Oxford County, but in looking at censuses for David and Rebecca McDaniels/McDonnel they do not have a child by the name of Corrine/Syrena/Cyrena.
I have several birth dates for Syrena (McDaniels) Harriman: her death record indicates born 5 May 1853 in Lovell ME and the 1900 census indicates born May 1854 ME. Berk Henley's transcription of her gravestone in Pine Grove Cemetery, Fryeburg, Maine, has a birth year of 1856. That's all quite different from your findings of a birthdate 23 Feb 1850! It's a bit mysterious!
Syrena/Cyrena/Corrine S. McDaniels is such an uncommon name and for 2 of the same name to have married a John Harriman would be pretty remarkable! There is always the chance that parentage as listed on a death record is wrong, but you can trace the Dean McDaniels family though the censuses of Lovell Maine and Syrena is right there with them in 1860 (as Syrena C.) and 1870 (as Serena). She is listed as Cyrina Harriman with husband, Sampson Harriman, in 1880 Fryeburg ME. I don't know why her death record would name her as Corinne S. when she seems to have used Serena or its variations in censuses, but that's what appears to have happened.
In tracing the children of David/Dana and Rebecca McDaniels through the censuses, I cannot find a daughter by the name of Syrena/Cyrena. Do you recall where you found the birthdate of 23 Feb 1850 for Syrena McDaniels? Where did you find parentage as David/Dana and Rebecca McDaniels? That might help as I would like to know if our information is incorrect. Berk Henley was family historian for the Harriman Family Association for many years and did excellent research. I maintain the HFA database from which I drew the information on Syrena (McDaniels) Harriman and corrections are always welcome, but I can't reproduce your findings. That makes me think we have it correct in the database and someone gave you incorrect information somewhere, but if your sources are better for parentage of Serena, then a correction may be in order.
Syrena/Cyrena/Corrine S. (McDaniels) Harriman lost her husband, John F. Harriman, early in their marriage. John Harriman died Oct 1877 and Syrena bore him a posthumous child, Bertha Harriman, in May 1878. Syrena then married John's cousin, Sampson Harriman. Syrena and Sampson are buried together in Pine Grove Cemetery, Fryeburg, Maine. John F. Harriman is buried in the Center Cemetery in Lovell Maine.