It's not surprising if she can't smell it, since anyone's nose adjusts to smells that it is exposed to for long periods of time.
What is your relationship with her, do you work with her or is she a friend? Because if she won't believe you that it is a problem, there is little enough you can do about it if you simply know her casually.
If you work with her, if the problem is terrible you could talk to the boss.
If you are having a relationship with her (since you mention the bedroom), you might be able to figure out if the problem is in her clothing rather than actually on her body. (Sweaters, in particular, can get a bad BO smell in the armpits. My little sister had this problem when she was a broke 20-something, since she couldn't afford dry cleaning. ALL her clothes smelled like the most awful body odor, and she couldn't tell.) If it's her clothing, can you offer to help her wash things and get things cleaned?
If she is merely a friend, I guess you could try having a heart-to-heart talk with her, but it's hard to say if it would work if she is unwilling to acknowledge that there is a smell.
That's too bad. Do you know if this is new? Sometimes body odor can change suddenly. There are certain underlying conditions more prone to excessive body odor such as diabetes. She may have an issue with excessive sweating which also can be medically related. There are actually different kinds of sweat such as the kind you get when you exert yourself physically but also the kind you get when highly stressed. Bacteria can get trapped there too especially if she is at all over weight. Using antibacterial soap to wash in the pits and elsewhere can be a good remedy. Her diet can be involved tool. Here's a whole article on it https://www.mayoclinic.org/diseases-conditions/sweating-and-body-odor/symptoms-causes/syc-20353895 . I had a teacher friend who had a student that this was an issue for. Mainly for him, it was hygiene related. So hard. You want to be sensitive but help. She bought deodorant and some antibacterial soap for him and left it with his things with a note saying that she cared about him and wanted him to try these things. How close are you? Could you friend her and say you are looking out for her, give her some deodorant?
I agree too that if you aren't washing the smell out of clothes, it can linger. Sigh.
I've got two teenage boys . I'm well versed in the bad body odor problems. I know it is hard to be around. We say "does anyone smell onions" as code for go do something about that.
I'd kindly see if you can help her. I feel bad or her. She indeed probably doesn't fully smell it anymore (nose blind) but also, may not know how to fix it.
Another possibility is if she eats a lot of pungent food, such as garlic and onions, it seems like those in particular come out really strongly in the sweat glands inside the top of the thighs where the legs meet the crotch. That location, she sweat glands really seem to concentrate smells that come from food. If this is the case, if she goes with you suggesting a solution, old-fashioned original Listerine (the amber-colored kind with natural ingredients like eucalyptus oil and menthol) is a good general skin cleanser, and especially seems to do a good job on the fats and oils in certain kinds of sweat that are hard to wash off otherwise. If she soaks a couple of cotton balls and cleans the skin there (avoiding the pubic area, it's where the legs meet the trunk but on the legs, not the pubes) she might be able to make the odor go away.