Friend makes plans and then dips

I have been friends with a girl from my gym for the past 4 years. She's a really kind person and we get along really well, she felt like a sister to me when we used to hang out. But for the past 2 years, she has changed a lot. She'll text me, then when I respond, she just vanishes for like 3 weeks. Then she'll hit me with a " I'm sorry, my phone didn't notify me". Or I'll be talking to her and something happens, so she says "brb, gotta take care of this" then I don't hear from her for a month. I'm getting really upset, because recently she's been asking me to meet up, and then she just doesn't follow up. Last Friday we agreed to go for a Sunday morning cardio run ( she's the one who initiated the conversation and asked me to). Then after we both agreed for Sunday morning, she said "I'll text you the exact time in a bit, cause I'm busy right now" . AND SHE DISAPPEARED AGAIN. Can someone help me out? Am I doing something wrong? If she doesn't want to meet up, why does she keep suggesting it?