There are currently two clips of Dolly's murder from a German-subtitled print of the film on YT, which appear to be minutely longer than the UK DVD releases/TV versions.
1) After the first slash, the scene cuts back to Anna as it should. But whereas in the UK versions, the shot cuts back to Anna thrusting the blade forward, here there is a fleeting reaction shot of Dolly and her bloodied neck (but with no apparent extra slashes) before cutting back to Anna thrusting the blade forward.
2) During the next shot in which Dolly is shown in close-up with the blade buried in the side of her neck, Anna's hand is seen to leave the hilt go so that Dolly is shown momentarily with the blade protruding independently out of her neck.
3) In the following assembly of rapid shots, there's one of Dolly staggering backwards towards the bath, intercut with another Anna reaction shot, before she is actually seen slumping down into it.
Now these shots are only momentary, probably adding up to an additional second at best; but it does however appear that there is different, more detailed footage of the scene floating around.
What it also does is to increase, in a rhythmic manner as noted by the OP, the identification between murderer and victim; in turn emphasising the savagery and balefulness of the attack. If the original sequence has indeed been tampered with by censorship, this would merely highlight the irony with which such meddling to 'dilute' on-screen violence can often make the situation worse by making murder and death seem more superficial and fantastical.
Jack the Ripper wasn't content to merely 'kill' his victims; their bodies were riven with multiple injuries in a manner suggesting a carthartic release of contempt and revulsion for the 'impurity' of human corporeality (which even more ironically mirrors the basis of most modern day moral crusaders' tirades against 'pornography'; perhaps begging the question of how far they would be prepared to go in the name of 'cleaning up' the entertainment industry...). Since Anna is meant to be transmitting her father's spirit, to have seen a full attack on Dolly in the way you describe would have further emphasised this and reminded us of the psychological context in which we are both perceiving the character and following the story.
The first murder that Anna commits - of Dora Bryn, is 'neither here nor there' in terms of pacing; it's the attack on Dolly that is IMO meant to 'reveal' that she is involuntarily and fatalistically perpetuating the utterly consumed rapacious lust for killing that her father possessed. Indeed, whilst Angharad Rees's performance is often slated; if nowhere else in the film garners such plaudits, the way in which she here migrates from a transfixed state to a raptorous expression of maniacally murderous glee is truly chilling to see. With the scene diluted however, it's more akin to a cheap attention-grabbing gore shot in a low-budget British horror movie than something more emotionally significant.
There's a UK Blu-ray release of Hands of the Ripper available from Network now.