Sindel/Alternate Timeline

Here is why I believe Sindel is not a retcon and that she is consistant with everything we know in the reboot timeline. As we know, everything before the reboot timeline takes place as normal from the original timeline. In both timelines Sindel is used as a trojan horse for Shao Kahn to enter Earthrealm. Quan Chi revives her and implants false memories into her to make her loyal to Shao Kahn. In the original timeline, Kitana is able to reach her mother and is able to convince her of the truth and with Shao Kahn's defeat, Sindel is freed from his control. These events do not happen in the reboot timeline.

In the reboot timeline Sindel attacks the heroes on Earthrealm leading to an all out fight where she dominates them. Kitana is taken out before she is able to convince her mother of the truth. Nightwolf then sacrifices himself to destroy Sindel, and succeeds. Sindel dies believing the lies Quan Chi made up. This means those lies are still present when she became a Revenant, and they were still there when she was revived in MK 11 Aftermath. Sindel is not a retcon because she is still brainwashed and thus is acting exactly like she was intended to be when revived in MK 9.