Booktagger

I read the book in the mid-60s (I was in 5th or 6th grade); it was one a series of maybe 3, set in WWII. Juvenile fiction, aimed at girls. Main characters: a girl with a widowed father, a NY-type CEO of sorts; the father's friend, an Army colonel in either Kansas or Oklahoma with 2 or 3 kids, one a daughter named Penny (?) and a son named David. The CEO sends his daughter to live with this Army family; the girls become friends, and she eventually falls in love with the brother; either at the end of the first or beginning of the second book he joins the Navy. No idea when it was published, or the title. The subject stuck with me because I was an Army brat, too.
Any ideas about this book(s)? I would love to find out if the books are even in print anymore.