Why has she struggled again and again to form a love relationship with a stable life partner? What is the best way to help her?

Here again, the primary driving force for this is karmic. She is had a series of lifetimes of failed love relationships. This is a mix of the culture of the day when most people were quite limited and corrupted to have bad habits, and to be less successful with interpersonal relationships. In addition to which, her own self-sabotage that started in prior lifetimes is trapping her into a kind of victimhood mode that makes her attractive to predators, but also makes it difficult for her to believe more fully in herself. This will result in her taking more risks. Not wanting to see the bad in others will make her more vulnerable to misplacing her trust and then setting her up for an even greater disappointment, having invested more in a given relationship than was healthy. And when it falls apart, blaming herself. This dynamic is not truly of her doing. It is a combination of the Law of Karma at work and the many, many, problems with would-be partners making it difficult to weed out the less acceptable candidates. The ideal strategy would be to do some deep subconscious channeling with trauma resolution for the issue of finding a reliable life partner, and help her to heal some inner roadblocks standing in the way of her happiness. That, in combination with the Lightworker Healing Protocol will help her greatly to have things work to your advantage. It is difficult for us to help her with her love life when she herself is closing off through fear within a deep part of her mind. This is essentially putting up a stop sign we must honor because it is still her free will, if only from a part of herself. So this will be the key to breaking things open and will enable her to be less encumbered and more objective in her assessment of the people she is with, and see with greater clarity and accuracy the true potential. And this will help her invest herself more wisely, as well as getting divine help more fully so those she meets who are available and might take an interest are there because they have been divinely guided to find her. That is how the majority of long-lasting relationships happen, to have this avenue closed is part of the problem here. So things will get better if she primes the pump in this fashion.