Boulter followed up her opening day win over Alice Gillan with a clinical 6-1 6-3 success against Arbuthnott at the all-British behind-closed-doors tournament in Roehampton.
The win sees the 23-year-old book her place in the semi-final, with Thursday’s clash with Jodie Burrage determining who takes top spot in the group.
Boulter, taking her first steps back following a lengthy back injury, is the favourite to win the tournament with Johanna Konta not playing and Heather Watson withdrawing on the eve of the event.
She hit Arbuthnott, who is ranked 954 in the world and was a last-minute addition to the line-up, off the court in a routine win.
“I thought I was pretty relaxed, I came out pretty strong,” she said on BBC Sport. “I am happy I closed the door and got the win.
“I am really enjoying being back on the court, to be back out here is pretty special and I cherish every minute of it.”