I would still respond to her texts, but not respond to them promptly. Because if you want to remain above reproach and avoid grounds for having a confrontation, then you probably have to keep up some premise of politeness. If you don't respond at all, she could always confront you on it, and since you're not good with that, here we go with the bullying thing again. However, if you respond a day or two later, then you can just say, "Didn't see this right away. Pretty busy lately...not a lot of free time."
I had a situation with a family on our kids' summer sports team. We liked them, we got along, etc. Then I started hearing some things from several different people (reliable) that some not-kind things were being said about us behind our backs. I didn't confront them, I didn't ignore them, but I dialed it waaaaaay back. If I saw them during the summer sports events, I'd smile and say hi, but not really engage much past that except for a very light conversation here or there. At the END of the summer, when I wouldn't see them anymore (haha), the mom FB messaged me and asked what was wrong; why wouldn't I talk to her? (Yeah, if it bugged her, why didn't she say anything all summer?) I claimed ignorance and pointed out several times when I'd had (light) conversations with her or husband. Never heard any more about it. Basically, if she was spoiling for a fight, I didn't give it to her. That was a few years ago, and I still don't talk to her much, but I have made comments about how big the kids are getting, etc.
With FB, just hide her from your posts. So it's not so blatant as defriending her, which could be grounds for her asking why you defriended her (another confrontation...ugh) but she just won't see anything you post. You could let her see the occasional post, just to make it seem like you don't have everything blocked. I do this with a family member who I don't want to know all of my FB business.
So in summary, pull back, be clueless, but be pleasant so she never has a reason to come back at you for anything. And if she's the kind of bully who tries to turn others against you, then she won't have a leg to stand on if you're pleasant to her. How can she complain about you being pleasant? If you do end up around her and she makes a nasty comment, just give her the blank stare or ask her why she said what she said, or ask her if she can repeat it (practice that clueless look).
And did she ever stop making comments about your car?