Disclaimer: this post is only for comparison and contrast between the two characters. I take no credit for Harry Potter.
1: Both are orphans. Unlike Harry, though, Alyssa was not a baby anymore when she lost her parents. She was 7, and therefore, can remember their deaths. She also got to know her parents.
2: Both are sent to live with their aunts and uncles, even though their godfathers were originally designated guardians. But Alyssa's life was far more sugarcoated than Harry's. While her uncle, Bruce was tough and unfair in the events of "The Frights of Fiji", he wasn't too extreme. He was always kind of like that, just not as much before Alyssa's aunt, Laura, died when Alyssa was 9. Aunt Laura was sweet, Hailey was close to Alyssa and on her side as well as similar to her. Alyssa also gets to move in her godfather, Alex, right after she turns 13.
3: Both discover magic's existence in their stories. Alyssa, however, is not a wizard in "The Frights of Fiji". In the sequel, "A Curse of Mayhem", she does get cursed with magic powers that she needs to remove since she can't control them. But in Book 3, she may become an enchantress permanently.
4: Both have wizards and non-magical people living in the same world. But wizards in "Magical Missions" are far more modern and don't hide from ordinaries. If anything, they want to fit in. One could see someone shopping or get to know that person and not know that he or she is a magician. There is also no specific term that wizards use to describe those without magic in their blood in "Magical Missions".
5: Both have evil wizards out to hunt them. With Alyssa, though, she has two different warlocks that she needs to overthrow, each in "The Frights of Fiji" and "A Curse of Mayhem".
6: Both Harry and Alyssa are kind of small and skinny for their ages. However, Alyssa was never starved or neglected.