Stinger:she is Cassandra "Cassie" Lang, the daughter of Scott Lang. Scott was the second Ant-Man, after getting the suit from Henry Pym, the original Ant-Man.
Although Scott Lang had never been a full-time super-hero, he was involved with big leagers such as Iron Man, the Fantastic Four and Heroes For Hire. So, Cassandra grew up with super-heroes. She had eeven been the romantic interest of Kristoff Vernard, the heir to Dr. Doom's throne.
Cassie and her father made some modifications to both Ant-Man's and the Wasp's costumes, for a project called "Project Stinger". She doesn't seem to have shrinking powers, because she didn't use them during their confrontation with Loki.