Hannah Field and Rose Fong make the step up from the Under-20 squad with England regulars Fran Matthews and Kim Oliver also in the squad.
England take on Sweden, Italy, Germany and France in their group and Maddocks is convinced his squad will challenge once again.
"We have got a nice blend in this squad. Both Sonia and Michaela are proven sevens players and they will lead the team well while the likes of Fran Matthews and Kim Oliver are England regulars," said Maddocks.
"This will also be a great opportunity for the likes of Hannah Field and Rose Fong from the England Under 20s.
"Although this is our one and only 7s tournament of the season we are determined to retain our title."