I think a cash gift should be joint, or the same amount to each. My grandmother used to give checks to her 2 sons and not to the 2 daughters-in-law. She would say to my mother "I love you like you're my own, dear, but the fact remains that you are not." Pretty sucky. I know that's not what you are trying to say, but you don't know what her background is with her own mother's receipt of gifts. So the cash is nice but if it's in 1 card, your DIL may feel that she doesn't get to spend it if your son puts it in his wallet. Some women just don't like to get appliances - it doesn't seem personal maybe? One year my father got my mother a set of pots and pans - and her attitude was, "What? So I can cook for you more efficiently?" It was, in his case, very sexist.
The main thing with gifts is to make sure they are purchased with that person in mind. My brother and SIL used to just buy a whole bunch of stuff (like 6 copies of the same bestseller) and 4 things made by the same charity workshop, and so on, and then sit there are the last minute and start assigning gifts to different people. My mother and I would open gifts and find that we got the same damn thing, over and over, year after year. So what you spend isn't important. If your DIL loves baths, get her a bath set. If your son loves socks, then get those. Make sure the cash is given in the sense of "You guys don't have a lot of money and I want to help" rather than "I couldn't think of anything and didn't have time to go out, so here you go." Sometimes people want to get things they wouldn't get for themselves - and if a coffeemaker either wasn't needed or if they would have bought it anyway, then getting it from you make take some of the "fun" out of opening a gift. If you have taken the time to get to know her and explore her interests and then have made a real effort to pick something out (whether in an actual store or on line if you really hate or have difficulty navigating the stores/crowds), she will appreciate it.
Again, I don't know what your DIL's experience is, how her parents treated the in-laws, and how her parents were treated by theirs. A lot of that goes into it. She may just need to feel that she's a special person in your life and worth your time to find just the right gift. You say in your SWH that "She should appreciate anything they do get, and I always say I just want hugs and kisses in return." So it sounds maybe like you aren't too fond of her, and almost like you are being a little bit of a martyr, saying you aren't into "things" and they are. Maybe that's not what you meant but maybe she's misinterpreting your sentiments the same way I am. And blending traditions from 2 families is a process, and they have only been married a year, so maybe everyone needs to work a little harder on understanding whether the other is coming from.