I received this quote while in the MTC. It is probably the most famous sister missionary quote I've ever read. It has such wonderful promises for sister missionaries in it and is by my favorite prophet, President Hinckley.
“Today many sisters are being called to serve. Many more are preparing to serve. Not because they aren't married or don't have anything else to do, but they have the desire to serve. One reason that the Lord wants more sisters to serve is because within the next generation He will send His priesthood army to the earth. He wants to send choice spirit children to mothers who have been prepared, properly trained, and taught in the gospel. What better schooling can a mother have than the experience and growth she gains through serving a mission.”
--President Gordon B. Hinckley
(I was told that this was given at a Missionary Conference back in 2004, but I don't know where or when.)