Pillinger completed the 3,004-mile cycle from California to Maryland in 12 days, nine hours and 14 minutes despite contending with hallucinations.
Her 2014 race ended when breaking her collarbone after falling asleep on her bike and it nearly happened this year.
"I did fall off once. I fell off on the same side in the same circumstances but luckily nothing happened," she said.
The 39-year-old IT worker from St Albans and daughter of the late planetary scientist Colin Pillinger finished with around 12 hours to spare in the early hours of Monday.
But she admitted that a lack of sleep was once again proving problematic.
"Unfortunately I have a habit of falling asleep on the bike and I fell asleep on the bike many times from half way," she added.
"We were doing 70 minutes (of sleep) per day plus some 25-minute naps to reset and some longer sleeps to reset which were spread through the race."
Gloucester's Ann Wooldridge came close to completing the race in 2009 when she reached the end of the course, but injury meant she finished a day over the time limit.
And Pillinger says that despite all the adversity surrounding her attempt, she is proud to have completed it.
"It's been something I've been trying to do for some time. The goal coming into this was to finish, purely because I have a nice big piece of metal in my arm and six screws from last year's attempt.
"Some people said I shouldn't have been on the start line so quickly, but this arm has been perfect."
Pillinger finished last of the three women in the Under-50 category, behind Switzerland's Isabelle Pulver and Joan Deitchman from Canada.
Ultra-cyclist Shusanah Pillinger has become the first solo British woman to complete the Race Across America.