Can you have a girlfriend trained by your predecessor?

First of all, the word training is not a good word, because it means controlling and dominating people. If your ex has coached your girlfriend, then this behavior may be a control behavior, which may have a negative impact on your girlfriend.

If your girlfriend has been hurt by her ex's behavior, then you need to seriously consider whether to continue to be alone with her. In this case, you need to communicate your feelings and concerns frankly with her and listen to her views and feelings. If she has stopped seeing her ex and is willing to establish a healthy relationship with you, then you can consider continuing to be alone with her.

However, if your girlfriend still keeps in touch with her ex, or is indifferent to your feelings, then you need to reconsider whether to stay alone with her. Under no circumstances should anyone be controlled or dominated, especially in a relationship.