It’s probably her clothes.
Some of them can be washed but the smell stays.
I would definitely try some hints first and then get more honest.
She’s new and this is going to be mortifying for her and so if you can tell her without saying it directly then that would be better.
I work with an autistic man who doesn’t get hints though and we’re at the point of someone having to say it bluntly but we’re reluctant because he has a lot of things going on right now and this might push him over the edge.
I would initially find out her background in a nice way.
If she’s a single parent with kids, then it may be a cost thing etc.
She could be living in temporary accommodation and can’t do any more than she is right now.
Being blunt to someone who cannot do any more, is not going to help the situation.
I wasn’t taught how to do laundry etc as my mum has MH issues so our clothes were rarely washed.
I moved out as a teen single parent and had to try and learn things as I went along.
I still struggle with the basics and what I don’t know, I don’t know I don’t know.
I thought that by me showering and washing my clothes on a quick wash it would be enough but then a few years ago I read on here about BO smells sticking to clothes.
I started washing on a longer wash (when I could afford it) and had to get rid of a couple of tops too.
If someone told me I smell, I would just wash myself, clothes and wear deodorant.
It wouldn’t get to the route of the problem and just cause embarrassment.
Whereas if you put out some hints then it may actually work better.
E.g. Just having a conversation with someone in front of her about how you/your DH/kid has been smelling recently and you couldn’t work out why because they’d been showering and wearing deodorant everyday, you realised it was the clothes and so you tried putting it on a long hot wash but then it still didn’t work and so you had to throw that top away.