At first, I was going to agree with the "tell her one more time" opinion....
But then I thought about it. No matter how clueless she is, you sent a clear message previously by not responding multiple times.
Bottom line - she's fishing. If she isn't an OW/former-OW/wanna-be OW of your X, then she's the gossip queen who wants to be able to provide some little nugget that no one else knows.
ANY response you give her will feed into that. Even just a "don't contact me anymore" will give her the idea that all this bothers you, and will feed whatever drama she is trying to fuel.
I see this because I lived it. My X wanted to be friends, he wanted... well, doesn't matter what he wanted, because I just wanted to be left alone. Especially since every time he contacted me, it would start out really nice, and then he would find some way of saying something that was a passive aggressive dig at me - more emotional abuse. He was good at being very subtle with it, in a way that to most people looked like he was being "nice". Honestly, I think he even saw it as he was being nice and I was just too sensitive and took everything the wrong way.
I finally realized that his intentions didn't matter - just what it did to me. And that I needed to stop him from contacting me.
And unfortunately, the only way to do that was to completely ignore him. No matter what he said, I just ignored. ANY acknowledgement of his existence started up things with him all over again, and reset the clock for how long it took for him to give up again.
So... give her nothing. I mean nothing at all. What you do depends on how persistent she is and if/how much it bothers you.
I went so far as changing both my home and cell phone numbers. I set up an e-mail filter so anything from him was treated as spam. If he went and got a new e-mail address, I added the new one to the spam filter. No FB yet at the time, but once I was on FB, I blocked him. With twitter I just had to ignore - and he had a girlfriend follow me and post crap too. Sigh. The few times he showed up at my church, I was fortunately either not there, or the one time, I was late & had to go straight to the keyboard up front because service was starting & was with now-DH (at the time, fiancé). Evidently, he decided to leave early.... A friend told me about it after the fact.
But as time went on, as long as I didn't respond the contact attempts became fewer and further between. It's now been at least 3 or 4 years since he has tried.
It's unfortunate, but with some people, the only way to stop it is to never, ever, EVER respond. No matter how frustrating it can be.
Check with your cell carrier - is there any way you can block texts/call from a certain number? I would block everything you possibly can - change #s if that isn't too much of a hardship for you. And just keep ignoring. As long as you don't feed it, it will eventually give up and move on.