No OP. Yanbu.
Your mother didn't think. It didn't occur to her that creeping around your house, late at night, in the dark, unannounced, no answer to her knocking, and essentially breaking in through the garage is actually incredibly frightening, when you have no reason to think it's your mother.
What would have really pissed me off, is it's one thing not realising she acted like this, but when she did see how it actually looks, and how rightly frightened you were, she got angry and defensive to try and justify what she did.
I did this a few years ago, and it was the same thing. It was dark, very late at night, all my downstairs lights were off, me and DC in bed. And there was this "tap tap tap" on the front door. I thought, who on earth is this at this time of night? Then I heard the front door handle being tried. I crept out of my room and looked on my drive, there was no car. No one I know lives within walking distance of my house. Then the tapping moved to the back door of my house, and I could hear someone very quietly trying the handle on that too. That was enough. 999 straight away. I was terrified, went in DC room and got him and hid in a big wardrobe together as the woman on the phone told me someone was being dispatched and to stay on the line. They were here in minutes. It was my fucking ex.
He "just wanted to talk" and hadn't called or text to ask first, because he thought I'd have said no. Had parked round the corner, on the road and not on the drive for reasons known only to himself.
The police weren't angry at all. And told me they'd rather people called them out and discover they weren't needed, than for someone not to call, and end up.... well, however. They were here and gone again within 5 minutes.
I was furious at him. It was genuinely terrifying. Of course it's not when you know it's your mother/sister/muppet ex, but that's information only they know. To you, it's anyone but them, because if they were planning on dropping by, unexpected, in the pitch black, they'd text or call first.
So basically, it's what do I do, if I hear someone I don't know, when I don't come to the door, trying to let themselves into my house, at night, and I'm alone with small DC in the house. You call the police.
I've got cameras up covering both doors and the driveway now. So I can identify someone innocently creeping around should that ever happen again. It never had before, and never has since, which again, tells you how normal it is for someone you know to be creeping around your house in the dark.