But first, she needs supplies.
How much does she pay for a standard typewriter ribbon? A specific price would be ideal, but even an order of magnitude would be useful. (5 cents? 50 cents? $5?)
Where does she buy it from? The drugstore? A stationery store?
How "inky" is it? (Modern ribbons will still leave a bit of ink on your fingers if you handle them, and I have a sneaking suspicion that the ribbons of 70 years ago may have been inkier.)
And, finally, what sort of branding does it have on the tin? (Name, colour, design, etc.)
*The story actually takes place in Arkham, but I figure Boston is the closest approximation.