Sister and surname for Foster-Rose

So, my main character is named [name_m]Foster[/name_m]-[name_f]Rose[/name_f], and I need a name for her sister. They currently have no last name, so that would also be helpful.

[name_m]Foster[/name_m]-[name_f]Rose[/name_f] is thirteen, and she’s a reader and daydreamer, she’s shy, smart,and she prefers to curl up with a book in her room or in the hammock chair than go be around other people.

Her sister is fifteen, and she’s more extroverted. She also loves to read, but she would rather be out with her friends. She loves riddles, and she exasperates [name_m]Foster[/name_m]-[name_f]Rose[/name_f] with her persistence. She also really wants [name_m]Foster[/name_m]-[name_f]Rose[/name_f] to be more social, so she drags her all over the place to parties and such.

They’re both homeschooled, their parents are basically stereotypical hippies, so they have interesting taste in names.

They have Greek, Czech, and [name_f]Sioux[/name_f] ancestry, if that helps with the surname.

Thanks for the help!

I think [name_f]Lilly[/name_f] [name_u]Sage[/name_u] [name_m]Stone[/name_m] could work. Or [name_f]Ivy[/name_f] [name_f]Rainbow[/name_f] [name_f]Summers[/name_f].