Pickens says by hand-delivering mail, supporters will circumvent reported problems with online submission forms, and avert any possibility that their emails get deleted or phones are left unplugged.
Pickens says she will personally hand-deliver each and every letter that supporters write by horse, in a nod to the historic Pony Express mail service.
"I am setting a goal of 20,000 individual letters to take with me," she said.
"This is a very important issue to hundreds of thousands of people that have pleaded with our government to stop gathering our wild horses," she said.
"This way, they cannot unplug their phones, make their website impossible to send a comment to, or delete emails. These are GOING to get to Washington. I promise you that!"
Wild horse advocates are concerned that fewer than 30,000 wild horses are left on the western rangelands. More are now held in captivity.
Pickens proposes a huge sanctuary, possibly in Northern Nevada, in which the horses currently held in captivity could be allowed to roam free. She said her plan would be more cost-effective for taxpayers and has strong tourist potential.
Pickens has set a deadline of September 1 to collect the letters.