I get the impression that you don't actually have a friendship here yet - what you've got in an acquaintance who is pushing for a closer relationship that you don't want.
I'd worry not so much about leading her on, as her not being willing or able to recognize that you don't want to be her BFF. Combine that with a negative personality, and it could take a *lot* of work to keep the relationship at the level you want it - FB friends, and the occasional get-together for the kids, but no joint family activities, no socializing with just the two of you.
Backing off completely may be the safest option in the long run.
My experience of people like this is that they end up in a vicious circle. They have some trait or other that make them unpleasant or exhausting to be around (negativity, clinginess, flakiness, poor social skills, emotional vampirism, drama queen tendencies) even though they're not a bad or malicious person. When someone gets to know them, they encounter this, realize they can't handle it in a close friendship, and try to back off. But the person really, really wants to be friends (because they've scared off all the other people they've met). So they push harder - calling more often, not taking no for an answer, responding to every single FB posting with detailed comments. Which of course, sends the target screaming off in the other direction at warp speed, ignoring phone calls, and blocking on FB.
Changing this dynamic is hard. The person needs to recognize that they are the problem, get feedback from someone they trust, and have known long enough to have them give this kind of advice, and to work really hard, often with professional help, on changing the dynamic. Unsolicited advice rarely make a dent.