Honestly, right now your local FB Marketplace is one of the best places to get machines. A lot of people picked up the hobby during the pandemic and bought nice machines, only to walk away when their lives returned to normal. A lot of them are now trying to sell those machines, and 5 times out of 10 they will even still have the original box.
One of the key questions that you should ask your DD is whether she primarily intends to sew woven fabrics or stretchy knits. If the answer is knits, the "old workhorse" machines are not going to be your best choice, because older heavy duty home machines almost never have knit stitches. I own 6 machines, 2 of which are "old workhorses"; these days I primarly use them to make home furnishings, and do everything else on my more modern machines. (I don't make jeans; I find that thrift stores have so many that there is never a need. I do hem jeans, but my modern machines are just fine for that as long as I use a Hump Jumper. The only thing I'd advise in this regard is that it is important to have the ability to change the height of the presser foot as well as the thread tension, and that the machine have a convertibe free arm to get pants legs, sleeves and narrow necklines around.)
If she will not have a serger available, then for knits, a regular machine really needs to have 2 special stitches available: a "lightning stitch" and a 3-thread stretch stitch; she'll be using them constantly if she's sewing knits. A mock-serger overcast finishing stitch is also useful for garment sewing, because it lets you easily stop seam allowances from fraying. Most importantl for knits, you would want to get a machine that comes with a walking foot attachment as part of the deal. As others have said, presser feet tend to be cheap, and you can even get big kits on
Amazon that work just fine, but a walking foot is complex, and can cost up to $250 depending on the brand; though $60 is about average. (A walking foot, btw, is a rather large gadget; it's about 1 x 2 inches, and looks like a hard plastic box with several moving metal parts sticking out at the bottom. I sometimes note that it looks a lot like a tiny Zamboni, and that fits, because in some ways it serves the same function: to make the surface beneath it even and smooth.)
On a machine that lacks a metal case, a metal-lined base plate with multiple screw holes on it for attachments is extremely nice to have for garment work, but if you don't have the screw mounts it isn't the end of the world; I have some that I just attach with masking tape.
Both of the modern machines that I use the most are Janome, which is a mid-level Japanese brand. (They also make Brother machines, so the parts for Brothers and Janomes are mostly interchangeable.) If I had the money I would love to invest in a Babylock, but with all the machines I already own (3 of which I inherited), I just can't justify the expense. The simplest difference between the Janomes and Brothers is motor speed: the Janomes are capable of a lot more stitches per minute, though they don't go anywhere near industrial speed. Nothing in this world is more frustrating to a sewist than a machine that only goes at putt-putt speed. It's nice enough for the first few weeks, but then you really want to get things done faster. My regular Janome has 3 motor speeds; I always use it at high speed unless I'm embroidering with it, but when DD wanted to learn I was able to set it to slow for her.
If your DD is the sort of person who really likes learning one-on-one, then buying from a local sewing machine shop is the best bet, because such shops always include hands-on instruction on how to use the machine you buy. They also will have a wide variety of models and price ranges unless they specialize in quilting or industrial machines. OTOH, if she's the sort of person who prefers to teach herself via
YouTube videos, then this aspect really is not as important.
One thing she will absolutely need if she's new to machine sewing: a good ergonomic seam ripper. No one ever thinks to buy one of these out of the gate, but they are crucial for fixing mistakes. A good pair of all-steel thread snips comes in handy as well, and can be had very cheaply. She will probably also need a good pair of fabric shears, &/or a nice rotary cutter and mat. (If you get a good price on a machine, throwing in an Amazon gift card for the purchase of helpful small tools is a nice touch; you can buy those things much more cheaply there than you can at a store like JoAnns, which is notorious for markups.)
PS: When it comes to good lighting, there is a very simple fix available quite cheaply: an LED sewing machine strip. These are made with adhesive on the back, and are sized to fit along the back lower edge of the throat space. You just stick it on the machine and plug it in, to get a very bright white light across the entire working surface.