You’ve mentioned American Girl - you know that there are mysteries for most of the girls, right? Those are a little longer, and there are also sets of short stories that you can find if you look hard enough in libraries or online bookstores.
Have you considered the ‘sequels’ to the original Little House on the Prairie set? Laura Ingalls Wilder’s grandson Roger Lea MacBride wrote a set about Laura’s kids, very similar to the first ones.
If she’s seven, all of the following are recommended as books for YOU as the parent to read and see if she would be old enough to handle them (at the most these could likely be read *to *her as a bedtime serial or similar.)
These are not recommended for her to just pick up and go at!!!
Gerald Morris writes a great set of books called the Squire’s Tales, where he elaborates on some of the great Arthurian legends and side-quests, usually with a pretty heavy moralistic/behavioral theme to them. They are really well-written, but I have not read one with a younger child in mind, so I don’t remember if anything gets too over-the-top - like I said, you’d have to check them out yourself first, and they may make a good thing for you to read to her, but I am unsure if they would be good for her to read by herself.
Likewise for the “Dear America” books. They are ‘fictionalized’ accounts from the perspective of a girl from some important point in US history, learning a historic lesson as well as usually a moral one. Generally written in diary or letter format. I KNOW some of these (Pearl Harbor, Vietnam War) are *very heavy *in content, while some are pretty lightweight as far as what happens in the plot. Most stories have an ‘epilogue’ of facts about the realities of that time-period, similar to the American Girl series. *Again, you’d have to carefully read through each title beforehand, but they are highly recommended, and something that a lot of girls graduate to once they are done with the American Girl series. (That means when they are usually OLDER than 7 - remember to check these carefully before considering them for your daughter!!) *
A spinoff is called the “Royal Diaries” and they are the same as the above, but with various historic princesses instead of random American girls. Same warning - check them individually because they’re written for girls older than seven!
My real suggestion here is to check with a first-grade teacher, or go to your library’s children’s section and ask if there is a children’s librarian who can help you pick out some new series. LOTS of things are being written now which may not be the most complex reads grammar-wise, but are still good stories that your girl will enjoy. They’ll know what’s age appropriate, and they can also steer you towards books which might be more complex and challenging to read, without being contextually overwhelming and too mature for her.