I'm glad she called and glad you picked up. You're right, you did need to hear her voice and talk to her; really, I'm quite proud of you for not being the queen of avoidance in this moment anyway!
I like the tone of what she is saying. And I agree, she has a point - it probably is good that something like this happened, to bring this up, so that it can be dealt with, cared for, soothed. Sometimes, or many times, it's the situations like these that strengthen and deepen a relationship, whether it's a RL one or a T one.
I understand why it feels so big to you, why it has shaken your trust ..... because it seems like this is big enough she shouldn't have forgotten it at all. (though I don't think she really forgot; she just had a brain fart! but it's easy for me to say this, because it's you in the situation. If it were me, I'd probably be struggling with similar hurt feelings and need help reframing it, too.)
However, I don't think, dear, that she has forgotten YOU! She knows who YOU are under this, and because she knows you so well, she knows how you need this to be handled by her, what you need to hear from her.

((As for you feeling guilty taking up her time with a phone conversation or whatever, I hope in time you can let go of the guilt sort of feeling that accompanies the legitimate need you have ..... and like she says, it is part of the service she offers, and it's her choice to be available for that sort of thing and offer that service. All you're doing is taking advantage of what is freely offered and that makes perfect sense .... if it's offered and you need it, use it! Without guilt or fear or shame ......
I do understand that feeling though - T2 spent hours on the phone with me (on occasion we talked in the evening for 1-2 hrs, depending on the severity of what was going on in my life/mind at the time). I was so amazed the 1st time I dared to call her and she wasn't in a hurry to hang up, but stayed with me. I made comments about feeling like I should pay her extra for that, a sense of obligation or duty to at least offer that. She said, I appreciate your thoughtfulness, but this is something I have always done for the few that need more time outside of session, when real life things are happening. I worried it was a boundary crossing, or even a violation ..... worried because T1 let her boundaries blur and did more for me than she did for others and worried this was some sort of 'special' treatment that would be taken away when T suddenly like she had allowed too much ..... but she made it clear this fit within her boundaries and within her interpretation of what her responsibility to me as a client and my needs entailed, and was nothing she would not offer to another client, if needed. After a while, I accepted that this something I needed, that she willingly made available to me use (not abuse) and that she trusted me to not abuse it - then I stopped feeling weird about it and enjoyed the security of having it if I needed it.))