Harper agreed to a five-year deal worth $750,000 annually, the school announced Tuesday. The former Lady Vols player replaces Holly Warlick, who was fired last month.
Horston, a 6-foot-1 senior at Africentric (Columbus, Ohio) and the No. 2 prospect in the espnW HoopGurlz Top 100, said Harper contacted her mother and promised to visit Horston and her family on Thursday.
"I don't know [Harper] yet, but I'm excited to meet her," Horston said. "Tennessee is not going to pick the wrong person as coach. I'm ready to go in there with open ears. I want to turn the program around."
Horston learned the news of Warlick's firing on March 27 as she was about to take the court for the McDonald's All American Game. Horston was named MVP of the game; she declined to comment on her future at the postgame news conference.
"There were a lot of mixed emotions," Horston said. "I was kind of upset but also excited about what's next. I want to win."
Harper, a native of Sparta, Tennessee, went by Kellie Jolly when she helped the Lady Vols to NCAA titles in 1996, 1997 and 1998 as a point guard.
"She was a point guard, and I'm a point guard," Horston said of Harper. "She has the blueprint. She's going to push me to be a great player.
"I believe she still has that 'Lady Vol' in her, and she's not going to let this program down."
Horston said she keeps in contact with most of the Tennessee players -- especially Zaay Green and Jazmine Massengill -- and they have indicated to her that the program is on the right track.
"I know the girls on the team now want to work hard," Horston said. "They don't want to lose. They are gym rats. They want to redeem themselves."
Saunders, the 2019 West Virginia Gatorade Player of the Year, said playing for Tennessee will be the culmination of a dream that has been years in the making.
As a freshman, she led Wyoming County East (New Richmond, West Virginia) to a state title. Three months later, her maternal grandfather, Gary Shrewsbury, died at the age of 68 due to cardiac arrest. Saunders used to go to her grandparents' house for dinner every Sunday after church. On many of those Sundays, she would watch the Lady Vols with her grandfather and the rest of the family.
"I wanted to make him proud," Saunders said. "If he were here today, knowing that I'm a Tennessee recruit, he would be proud and happy."
Given that personal history, Saunders was not deterred by the coaching change.
Saunders said it was "upsetting" and "very sad" when Warlick was dismissed. But she was thrilled when she found out Harper had been hired.
"I love that it's staying in the Vols family," Saunders said. "We're keeping the tradition alive.
"Transferring never occurred to me. Tennessee has been my dream school since I was 8 years old. I grew up watching Candace Parker and Tamika Catchings."
Key, a senior at Cary (North Carolina) and the No. 46 prospect in the Top 100, she said she committed to Tennessee for the school and not only for a particular coach.
"I wasn't happy to see Holly go," Key said. "I heard a lot of talk on social media during the season, but I didn't think Holly was going to get released until it actually happened.
"It surprised me. But ... I want the program to get back on track. I have never had any doubts about wanting to attend Tennessee."
Key said she woke up Tuesday morning with a mountain of text messages from friends and coaches, all telling her that Harper was headed to Tennessee.
Harper called Key's mother, and the two are working on a time when the coach can visit the family.
"I want to meet her," Key said. "I want to talk to her. I'm looking forward to getting to know her. I'm moving in at Tennessee at the end of May. I'm excited."