Your mother should receive PAL (Passed Admissibility) after the last step she reached. PAL indicates that eligibility is passed, information sharing is complete, medical checks are OK... In a nutshell, everything is passed except Security screening. After PAL, the security screening process begins, which has a highly variable duration - it can take anywhere from a few months to almost 2 years, especially if it's an "enhanced" or "comprehensive" screening.
You didn't mention in your post whether your mother received PAL or not. If she has received it, that means she is now undergoing security screening. If not, she is still in the eligibility assessment phase.
Normally, it takes about 6 months after ADR (Additional Document Request) to receive PAL. However, since you mentioned the ADR was a year ago, this may indicate that your mother's file is currently on pause because it's not being prioritized (please refer to Iceforest's recent posts above for more context on prioritization).
Lastly, I should emphasize that this is just informed speculation based on typical processing patterns. Nobody knows exactly what is happening with a specific application except the immigration officers handling the case.