There's a fantastic book called Love Me, Don't Leave Me that deals with issues such as this one. The great part is that it has exercises your can do to learn more about your behavior and where it comes from.
I think just the sole feeling of knowing you are ACTIVELY working towards being better will give you asense of comfort to combat a bit of the anxiety.
First, if I may ask, is counseling not an option due to finances? While I know that it can be expensive, there are many therapists who offer sliding scales options for payment and that can be a big help.
For you to provide some help for her, I'd recommend you encourage her to take care of herself. Many people with abandonment issues suffer further by neglecting self care.
They need to make sure their emotional needs can be met and that they can meet them themselves, which helps them show up for those they love.
Be present for her. Actively listen to her without distraction.
Reflect back to her. Summarize what she's told you so she knows you've listened and you can be more understanding of her position.
There may be times when she doesn't know how to articulate her feelings and the complex emotions she's experienced. Try to help her identify those feelings and help her communicate her nuanced emotional states.
Normalize her fears. This is done by acknowledging the fact that other people have also experienced abandonment and suffer from it, as well. It will help her realize that she isn't alone and this isn't abnormal.
And please, avoid unhelpful responses like "everything happens for a reason" (that is minimizing), "things could be worse," or "you turned out fine, though!" Those phrases offer no substance and emotional value. Just avoid that like the plague.
You could also help her draw up a feelings wheel if she has trouble expressing her emotions. This is a therapeutic technique that can be largely helpful for assigning appropriate words to our emotions. It touches on primary, secondary, and tertiary feelings so it can be very beneficial to have one. You can download a wheel and use it if you'd like.
For resources, she can look into self help books, such as these:
• Cognitive Behavioral Therapy Made Simple. This book will be a great supplement for therapy and can help your friend learn to self soothe and manage her feelings.
This book has saved my relationship life. I feel like it will address your trauma and relationship issues as well. Love Me, Don't Leave Me:... https://www.amazon.com/dp/1608829529?ref=ppx_pop_mob_ap_share