I wonder if maybe your T has done something that you're not acknowledging your angry about? Has she said or done anything that reminds you of your mum, has there been a recent lack of attunement between you and your T? The slightest and silliest of things can evoke the need to protect yourself from pending abandonment. Have a real good think about when these fears started becoming strong again and see if there has been anything between you and T that could account for it.