Mitchell was over 20 seconds ahead of second-placed Anna Tait as she won in 4:16.20 - cutting 0.88secs off her previous best.
Her time was only 1.20 outside the qualifying mark for the European Indoor Championships in Belgrade in March.
Given that it was a solo run, Mitchell looks capable of achieving the mark.
Meanwhile, Kerry O'Flaherty finished fourth in the 3,000m at Sunday's City of Manchester Indoor meeting.
Running after being bothered by a virus for close to a month, O'Flaherty clocked 9:18.06 - just under seven seconds outside her indoor personal best set last year.
Swansea runner Elinor Kirk won in 9:00.59 which left her well ahead of Charlotte Arter (9:12.47) and Lauren Howarth (9:15.83).
Banbridge athlete Emma Mitchell continued her impressive winter form as she set a new personal best in winning the Scottish Indoor 1500m title.