Putting Serena in SM right now is the worst thing you could do with her. I like the fact that the first leg of SM is dedicated to foreshadowing and setting up future plots and dynamics. If Serena inserts herself into the series now, she'll damage the flow of the series. She'd be a glorified filler arc character. The attention would shift from the new characters like Lillie to Ash and Serena, a plot I really don't want at the point and time.
"Everyone creates the thing they dread. Men of peace create engines of war. Invaders create Avengers. People create... smaller people? Er... children! I lost the word there. Children. Designed to supplant them. To help them end."
"Resistance. Rebellion. You will burn these ideas away."
But this is the traditional royal Canterlot voice! It is tradition to speak, using the Royal "we", and to use THIS MUCH VOLUME WHEN ADDRESSING OUR SUBJECTS!!