Parker can’t remember a time when she didn’t dream.
Let’s rephrase that, she can’t remember a time before her dreams gave her insight into a parallel universe. It wasn’t until she was 12 that she realized her dreams weren’t normal; that they were too clear. It wasn’t until she was 15 that she even decided to look into the phenomena she was experiencing, and came up empty handed. It’s not like there’s a guidebook on interdimensional cerebral communication in dreams, and if there were, she certainly wouldn’t have believed that’s what was happening to her, at least not back then.
She can’t remember the first time she saw Parker II’s world, but she remembers the first time she saw it after Emmet died. Typically, in her dreams she would be doing normal, everyday things with Emmet and her family. Sometimes they all ate breakfast together, sometimes they all went to the moves, and sometimes they had family game night. But this dream was different.