The 58-year-old walked 21 miles from Laxton, in East Yorkshire, to Thorne in Doncaster, on Saturday with comic Alan Davies for company, and yesterday she trekked from Thorne to Harlington with TV presenter Gabby Logan.
Today - day four of her challenge - she is due to make her way from Harlington to Langsett.
She said: “Every morning I sit here smiling and looking forward to the day.
“By four o’clock a dark vacuum has fallen inside my head and a great fat gloom descends upon me. All I want to do is lie down and cry but I won’t because I refuse to cry in public. So just imagine me up in my room at about 11pm, sobbing and holding my leg.”
The BT-sponsored challenge will see Brand climb to 1,500ft across the Pennines as she walks from dawn to dusk for seven days, burning around 6,000 calories each day.
The journey will be recorded for a BBC documentary to be broadcast in the run-up to the Sport Relief weekend, which is taking place from March 18 to 20.