AITAH for nagging about $$ owed to me?

Last Tuesday a coworker of mine was asking around because she needed a ride to a dentist appointment that afternoon. She was going to be getting anesthesia and didn't want to drive herself. She was asking around and, with no luck from others, eventually asked me, offering to pay me for my time. It's mainly because of this that I agreed to help her.

Her appointment was at 315pm so I needed to pick her up at 3pm. I was at her house by 230 and she didn't come down until about 3pm. No biggie.

Her appointment was about 15min from her apartment. When we got there, she told me that it would only be about an hour long appointment. Again, no big deal. I decided to do some errands while I waited. Around 345pm, she texted me and said she was just then getting brought back. I was a little frustrated but I was her only ride so I just shrugged it off.

Around 421, she told me she was finished. I picked her up and brought her home. Before she went in, SHE asked how I would like her to pay me. I suggested $20 and she agreed (NOTE: She is well paid so $20 is pocket change to her).

Unfortunately, I don't have Venmo (my credit union isn't compatible) but she said she had cash upstairs and she'd bring it to me tomorrow at work. That was my first mistake; I should've made her get it and bring it down. But, I agreed because she hadn't (yet) given me a reason not to trust her.

Well, Wednesday came and she said she forgot the money. She said she needed to break her big bill so she'd bring it on Friday. Friday came, and Friday went. By the time I left work, she was gone. I don't like bothering people about money, even if it's money they owe me, so I didn't message her until about 30min before I went home. She's normally around for most the afternoon but this day she had left early. I told her that I would just get it from her on Monday.

Today is that Monday. I've scheduled a reminder text for her around 8am which is an hour from now (I don't want to ask her about it in front of other coworkers...but at this point, I'm thinking I should). I'll let you know if/how she responds.

I'm just wondering AITAH for bugging her about it? It's only $20 but in today's world that's a whole tank of gas 🤷‍♀️ It be one thing if I had offered her the ride, I wouldn't be so annoyed about it. But she asked with the intention to pay me. At this point, I'm thinking she never had the intention to pay me and only offered $$ so I would agree.

What do ya'll think?

UPDATE: I sent her a reminder text this morning asking her if she was ever able to get the $20. And she replied, "I thought it was $15?" (I can't remember at this point honestly) Whatever it was, it's the fact that she can remember how MUCH it was...but hasn't paid me back yet? Ridiculous. She said she'll get it to me today but I'm not holding my breath.