The Page Three star, still best known as Jordan, caused chaos in the small market town of Olney when about 500 people turned out for the launch and book signing on Saturday.
Florence Wood, an 11-year-old from Raunds, was one of the first in the queue to buy a set of pink bandages for her pony Carlton.
She said: "I love the clothes because they're pink, and I only wear pink when I'm riding Carlton. I wanted to get Katie to sign a picture of me on my pony."
Amber Hayfield, aged 16 and from Olney, added: "It's really exciting that Katie Price decided to come to Olney, it's probably the most exciting thing to happen here.
"I really like the design of the clothes and think Katie is really cool so it's brilliant to get the chance to meet her."
The queues started forming outside Derby House saddlers, where the launch took place, at about midday and Katie did not appear until 3pm. Those at the back of the line still faced a two-hour wait to get their books and new clothes signed.
Derby House commercial director Mark Reeves said: "Katie's range of clothes has been the most successful we have ever stocked.
"It's got a really broad range of appeal so we have had a lot of teenagers coming in to buy items but there has also been a lot of interest from older people. It's particularly popular among younger girls because it's all pink, but a new range of other colours will be launched for the autumn which we hope will be just as successful."
The new range, named KP Equestrian, went on sale at the Onley store before the signing and organisers said several hundred items were sold in just a few hours.
Speaking of the her new clothing line, Katie said: "I've had great fun putting the range together and it's been brilliant doing it with my own company.
"I know all the girls are going to love it, and not just the horse-mad ones, there's something here for everyone."