What is the reason my new client is having trouble with her love life, with many short-term partners who move on, and come back expressing interest only after they have already committed to someone else, and she is alone and childless at 48 years of age?

This is a problem that is karmic in origin, having had a series of lifetimes of unrequited love and unstable love partners who abandoned her. That wounding has created a situation where the accumulated grief and sorrow from living a loveless existence has carried over that energetic signature of victimization in the current life, and this creates a match to potential partners who fit that very profile of having difficulties committing and having a deep long-term relationship that is stable. This is the way heavy drinkers end up marrying alcoholics. It is not only that they often meet such individuals in a bar, but that the Law of Karma will pair up such individuals because they fit together so perfectly, with their vulnerabilities and inherent self-destructive impulses. This is repairable with deep karmic repair and can be worked on further to change your overall energetic signature to remove this obstacle.