Hi Kevin,
Your bike is definitely a prewar Murray-Ohio built girl’s Pacemaker. Murray sold them under the house brand of Mercury and through other retail outlets branded specifically for the retailers. M-O introduced the design at the 1939 World’s Fair and it was produced through 1941 and probably into early 1942.
The ABC Services publication of a booklet of serial numbers used on Western Autos bicycles has been helpful in several areas with regard to dating bicycles made for Western Flyer by several manufacturers and inferences can be taken from that information and cautiously applied to similar models built for other suppliers. I believe the key in this case is the letter “E” in your serial number which I believe is a year signifier. My speculation at this time is that it shows your bike to have been produced in or for 1940. That date aligns with the bike you have but the source information I am deriving my estimate from says nothing about the subtleties of model years vs calendar years and if the dates refer to orders taken, the factory completion of bicycles, or the delivery of the bicycles to the retailer.