If you are in New York, the original Broadway production is archived at the New York Performing Arts Library. Fantastic cast.
Though I have to say that even more than musicals, it really doesn't work to base a performance off of someone else's work in a play. Thomasina's scenes have so much to work with. Your friend should put in the time and really created a full interpretation from within. If your friend finds what she has in common with Thomasina and brings that to the character, it's going to ring much more true than if she just copies Jennifer Dundas performance.
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