[Artemisia] period music?

[Reuben and Arwen]

Thanks for all the useful replies everyone!  I never knew vibrato was such a controversial issue. 

Disclaimer- I was posting on Sarah's behalf because she was off babysitting and couldn't post to the Aerie herself.  I can carry a tune but I'm no singer :) She was trying to find information on period singing and not finding anything definitive on the vibrato question.  Her mixed choir teacher, Dr. Mikelson at Helena High, strongly encourages vibrato almost all the time, so it is very hard for her to eliminate it totally.  She has been toying around with singing "Oh Mistress Mine", the version from the album "Elizabeth's Music" by the Baltimore Consort.  She has sheet music for a choral arrangement that I'm pretty sure is modern.  The melody line is very different from the Baltimore Consort one.  How is the Baltimore Consort version for authenticity?  

Esther