Bob Parr: Why would they change math?
Violet Parr: I hate superheroes, and I renounce them.
Screenslaver: Supers are no longer in control... I am.
Winston Deavor: Help me bring supers back into the sunlight. We need Elastigirl.
Rick Dicker: If you wanna get out of the hole, first you gotta put down the shovel.
Dashiell 'Dash' Parr: Wait, I thought you renounced superheroes.
Violet Parr: Well, I renounce my renouncement.
Screenslaver: You don't talk, you watch talk shows.
Helen Parr: I missed Jack-Jack's first power!
Bob Parr: Actually you missed his first seventeen.
Edna Mode: Done properly, parenting is a heroic act... done properly.
Answer: I think the fact that Evelyn from Incredibles 2 and Roxanne from Megamind bear some similarities is purely coincidental. The idea that there may be a hidden connection between the two is unlikely and the idea of them being related is even more unlikely. It should be noted that Incredibles 2 is a Pixar production, and Megamind is a Dreamworks production, so the two aren't even made by the same company. Perhaps, her design was inspired by some features of Roxanne, but the idea of the two being connected or related is pretty doubtful.
Casual Person