Glad to see you've / dh /cafe owner reported it and police are being supportive. They both deserve it.
I'm not glad that this happened, please don't think that. But given the way they both seem to be all sorts of crazy and given the mum was happy to do this in front of her friends, she sounds crazy enough that you can imagine that she has been planning or fantasising about doing something like this if she bumps into you.
So given that there has been a strong possibility that something was going to happen, it's excellent that it happened in this cafe that has cctv to record everything, that the cafe owner - who doesn't particularly know you other than as an ordinary non-coffee-pouring customer - thought it so wrong that he contacted the police himself and has kept the cctv specially, and that the community police officer it was first reported to agreed with him and thought it was something worth following up.
Even though you too are reporting, the fact the cafe owner reported it first means that they can't accuse you of ruining their lives even further by going to the police because somebody else did that.
If this had happened elsewhere she could have hit or tripped you or thrown something over you or who knows what - with no witnesses (or worse, her friends that would have twisted things) or cctv. So if something was going to happen it's good that it happened the way it did.
I wouldn't reply to the text message but I wouldn't block her just yet - if the police do go around for a chat or more, chances are she will send more text messages that will be similarly loopy and will give more evidence to show she is unhinged and harassing you. Plus give a heads up if she threatens anything else.
Then when you have had enough you can reply to one message with a quick 'please do not contact me again, if you do it will be harassment and I will go to the police' reply that means if she does try to contact you you can escalate it to the police.
Hope it all goes well when you do your actual report!