You know you are the problem, right? You trained her to rely on you no matter what, you taught her you would be there. She took you at your word and more importantly, your actions.
To undo this you have to take action. You have to decline calls from her, decline being available, decline being able to drop things to rescue her or even just to talk. Wean her down to the amount of time you want to give to her, and hold that line hard and fast.
Start with not answering when she calls. Do not call her back for at least 4 hours, then 6 hours, then 8 hours, then the following day, the following week, etc..
Do not say yes to driving for running errands or to just chatting. You are in the middle of something for a family member, for whomever, you cannot do this. Recommend she call a car. Refer to the paragraph above, just don't answer the phone until many hours later.
If you are roped into driving her, set a date and time and a fixed unbreakable limit on how long you can be out and away from what you need to do.
If you are going to pick up the phone for her, set an alarm, make it loud. When it goes off, quickly get off the phone, "Oh my God I have to go." You do not have to explain, just hang up. Next call, "I forgot about an appointment." Then hang up quickly before she can ask questions.
Do not answer every text, not even with a smiley face. Be very selective about the texts or emails you answer.
If she shows up to your home, put a timer on it for no more than 30 minutes and then grab your keys, walk out, get in your car, drive away. Wait until she's gone to return.
If you want to keep the friendship, schedule things to do that are short such as coffee, a walk, whatever is short, but get it in a calendar with a fixed start and end time. Do not be available before or after.
Most important rule: stick to it or quit complaining.