Well what I sometimes do is have the dust bath cage out during playtime, and then close it when they are done but allow them to play longer. Here is a little video of them dusting in their "bath cage"
https://www.youtube.com/watch?v=ES_H3-3TamQ (I put them in there while I clean their cage too so try don't get into trouble). For you just have the dust bath out and take it away once she is done, and allow her to hop around and play for a bit longer. That way they shake most of the excess dust off themselves before putting them back in their cage. There really is no way around the dust though, you can also try sweeping or vacuuming the cage a little while after she goes back in to get rid of the extra dust on things.
You should not brush or comb a chin right after a bath, it can cause you to pull out fur. Also brushes don't really work on chins, their fur is too thick. You need a fine toothed comb if you are going to groom her, you comb tail to head, and comb before a bath so all the loose fur ends up in the dust bath and helps the dust get all the way to the skin. Unless you are showing her or she got something in her fur, combing is not really necessary though, most chins don't like it.
As for peeing on shelves, that is a pain, you need to make sure you really clean up the pee or she will just keep going there. I don't know what kind of shelves you have but if they are metal just scrub the area down with some vinegar and water. If it's wood you may need to sand down the area where she pees in addition to using vinegar and water to get rid of it. If it's soaked into the wood too far to just sand down, you may need to replace the shelf. Oh and with litter boxes, you have to put them where they want to go, most instinctively pick a corner/spot to pee and then you just put the little box there. They aren't like cats, that prefer to pee in the box, chins don't care, some never even get the hang of it, and some will simply stop using the box for no apparent reason. My current two just take a couple steps from where ever they are and pee, luckily though they do go to the edge of the shelves to pee, so it ends up on the cage bottom most of the time, but other times it ends up on the floor outside cage :facepalm:.
Pee stains on the chin can be cleaned up with dust baths, just add a little bit of corn starch, about a teaspoon, into the dust to help remove the staining. It wont be a quick fix, but the staining should lighten over time with each bath once she stops sitting in the pee.