Well, the thing to stablish is where exactly the blood is coming from: if it's IN her pee, then it's probably an infection (of her bladder/kidneys) - I had them a couple of time in my last pregnancy quite bably and never had a temperature, and my bloods were 'off' but not really typical when it comes to infection. However, I responded quicly and well to antibiotics so it was indeed an infection (I also had ++ketones although it's more likely her hypermesis causing your wifes)
If it's coming from her cervix, then given she has hypermesis I would say it's likely (hey, Im not a doctor, but on my fourth pregnancy with experience of bleedin with two of them!) from the fact her cervix will be sensitive due to all the extra bloodflow to the area and, for som women, even having a bowel movement or continued retching (hello, hypermesis) can cause a small amount of superficial bleeding.
It's obviously a small amount as it's brown.
Ok, so she/you need to bring this up with the team looking after her, so that they can investigate, but in all probability it's either her cervix or easily treated. I know it's easy to worry but it's really unlikely to be anything as sinister as miscarriage given the hypermesis, that it's brown blood and the absence of any cramping (you didn't mention it,so I assume she's not cramping?)
But, again, bring it up with the team. Don't wait for rounds to speak to a doctor, tell one of the nurses/midwives. And then chase them up! (because, sadly, as I'm sure you've seen, they're often rushed off their feet 
)