How can I help my friend who is in a downward spiral?

I have known my friend for over five years, in that time she has consistently shown signs of depression, substance abuse, anxiety, and self destructive behavior. In recent years she has seemed to make improvements. She has been happier, able to retain employment, more motivated, and even going to therapy. In recent months I have noticed that she has become increasingly negative. She is about to lose her job because of being late, she is showing up to social event drunk, she is being overtly hostile to people at parties, in restaurants and towards her roommates, and she is throwing tantrums like throwing chairs around because of a simple frustration, pouting, crying, or giving the silent treatment to friends if she doesn't get her way. I have told her that I am worried about her and that she is not acting like herself and she has acknowledged that there is something going on. I am not sure how to help her from here though? What do I say or do to help her? A group of our friends are planning on going on vacation this summer and I don't know how realistic it is for her to come along. I don't want to make things worse though.