I think Marda's advice of being proactive in both addressing the issue to the Management, gaining advice from local law officers, and possibly seeking mediation are all spot on.
I just wanted to comment that there are a lot of gray areas. You don't mention the age of your grandson, nor the complaint of the other tenant in question. Several things came to mind when I first read this.
First, living in a communal-type area such as an apartment complex does involve a lot of in-the-moment problem solving. Certainly, this tenant should not have been taking pictures of the child. This sort of restriction SHOULD be brought up with the management; there should be some sort of privacy guidelines. Unless one is recording a crime in progress or criminal activity, there's no reason to be taking pictures/video of any other person without their/or their parents express permission. I would certainly advise your daughter to bring this up, as I have the feeling this may occur again with other tenants.
There's a lot of give and take, as I said. Something I've learned over the years as both a nanny and mom is that there are a lot of children playing in a relatively unattended way at parks and in public areas. I call this 'relying on the village'--when we send our children outside to play without our presence (that is, outside of our sight or hearing), we are more or less trusting the world with our kids. Sometimes, we don't like the results. I have joked with my neighbors that if my son (when he's much older) is doing something unsafe or disrespectful, "please, yell at him" rather than letting him continue doing the dumb, rude, dangerous thing he was doing.
On many occasions, people have chosen not to attend to their children, and have become angry with me when I've chosen to make boundaries with their child. When a child, unattended, is acting out, it's not appropriate for the other adults to let it continue. I've gotten the stink-eye from more than one parent who was angry with me for parenting their child when they simply couldn't be bothered because they were across the park, too wrapped up in conversation or of the opinion that *their* child is never the reason for conflict and doesn't need tending to. I am very age-appropriate and guide in a non-punitive way, and if I'm walking your child back to you, it's because you weren't parenting your kid. Period. I don't feel badly about it, because someone has to watch the kids and if you are forcing me to watch your child, that was your choice.
If it were me, I'd also make some agreements with my child about where it is safe to play, give this woman's apartment as wide berth as possible, (no need to goad) and come up with a plan to follow if she becomes upset at him again. She may have other problems (physical or mental health issues) that your daughter isn't privvy to, but might want to assume she has, as this woman has questionable skills in resolving conflict.
If it were me, I'd also just come out from time to time and 'peek' on the kids playing. What kind of activity is going on? Maybe the kids are being too loud or disrespectful outside of "mom's" eyes. The problem with not attending our children is that we don't actually know what's going on when these incidents are happening. If a child is younger, they need to have an adult present, period. If they are older, acting more mature and showing good judgment on a regular basis, that's when I'd be more comfortable in letting the children play on their own. Every parent has to know their child enough to know when they are capable of monitoring themselves without constant adult supervision, and every child has their own time for this. (Even kids who did fine alone for a while sometimes regress and need adult company from time to time.) There's no fool-proof age for this.
Hope this resolves itself soon! The weather's too good not to play outside!