Toxic Friend?

One of my close friends has been giving me issues lately. I sent her a birthday card and gift since I felt like I didn't give enough to her for her birthday, but she said nothing about it even when I asked her about it. When I talk to her, she does an emotional 180 from being all happy and excited when she talks to my other friend to being upset and mad (even when I haven't done anything) towards me. She used to be amazing to talk to and would be really nice towards me, but now I feel like she hates me despite me not doing anything wrong towards her. I'm for sure that she probably talks behind my back. She and my other friend were all I had and now I feel like somehow she completely flipped on me for no apparent reason. Is she toxic? I feel like she's sucking my joy away from me for sure now which is making me feel horrible physically and mentally. How can I distance from her without anything bad happening?