Thread a flexible needle (usually called "circular") or a wire through a full row near the cut, unravel the remaining rows, then take a fine crochet hook to chain the loops together.

Or just hem it, but that doesn't look like what she does.

Circular knitting typically uses a technique called "grafting" or "Kitchener stitch" to close tubes seamlessly without unraveling - you'd temporarily secure stitches on holders, cut one strand, then use a tapestry needle to mimic the path of the yarn through the live stitches.

Take a look at the next T-shirt you put on. Or socks.

Can I ask you to expand on this?

I've never worn knit socks, and I don't think I've ever seen a knit T-shirt, so I'm not quite sure what to look for (or at) :)

You've likely worn knit socks and T-shirts -- they're machine-knit. A lot of clothing is knit, not woven. Fabric does not have to use big and chunky threads to be knit; the loops can be quite a small gauge in size.

Ah - that makes sense.

I was thinking of hand-knit clothing, which (as you say) tends to be big enough and chunky enough that you can see the stitches.

TIL - thanks :)

You can take a magnifying glass to any old t-shirt you have around. Or these days, you can also just take a snapshot with your smartphone and zoom in.

Compare with what you see on jeans and dress shirts, polo shirts, dress pants, socks, etc. It's quite interesting.

I don't think I've ever seen socks or T-shirts that weren't (machine) knitted. Knitting produces more stretchy fabric than weaving so it's better for garments that fit closely.

Yes. Dress shirts and jeans are common examples of woven fabrics.

There are also some technical fabrics that are neither woven nor knitted (nor crocheted) fabrics. See https://en.wikipedia.org/wiki/Nonwoven_fabric

They might be sergering the edges.