First of all, do you feel ready to work on abandonment and trust issues? Because those are really big and heartbreaking things to tackle and all that is stirred up in confronting it might trigger your OCD stuff again.
Secondly, if you are ready to really get into that stuff, i think you need to be realistic about whether your old T is the one to help you with this. You might think she is because you yearn the closeness and nurturing that she offered you but trust me, going thru abandonment crap sends you down a crazy road and it is really really important that you have a T that holds good boundaries. I know it's not what you want to hear, cos honestly i don't like the fact either. But constant access to a therapist keeps you in a place of neediness and dependence and never really trying to cope yourself. There needs to be some space in the week where you cope without her, because it is the only way you will learn resilience. And if she can't recognise that and doesn't hold the boundaries it can be really dangerous and harmful for you because what you want to deal with is Trauma. Is she qualified to work in depth with trauma, attachment, and everything else it entails?

If you've truly considered all this and you still think she's best for you, then really isn't it your parents you should be speaking to openly and honestly about what it is you want to work on and why the old T is best for you?