I think the Darla of BtVS fits very well with the Darla of AtS. When we first meet Darla, she is seducing a victim, and she repeats this tactic later. On AtS, we learn that Darla made herself a small fortune as a sex worker. Seduction is Darla's main weapon against Angel both in the BtVS episode "Angel" and on Angel the Show.
We also learn on AtS that Darla favours brains above brawn. Her foil in the master's court is Luke, who is this big brute. Darla tricks Buffy into thinking Angel attacked her mum, and then uses guns to fight Buffy. On AtS, Darla murders all the senior members of the special project division, except for Linday and Lilah, who she plans to use as her stooges inside the organisation. She also starts building an army of more brutish demons.
Both on AtS and BtVS, Darla is quite subservient towards the Master.