Actually, that's a hard question to answer. I'm pretty sure that she is in care of all the stuff because she's sitting on the back of the steed - it would be a tad unfair if he had to carry the things and walk. Then, spinning is the typical female work that can be done in between, at about any time, and can be done in short slivers of time, a few minutes here and a few minutes there. So... looking at the picture, I'm not convinced that it is showing an actual travel situation. The distaff has to be held up by something, since she is not holding it; however, the thing is perfectly upright. Then I imagine it's a bit awkward to spin across the baby's travelling box/bed, like she does, all with the right arm being hindered by the carry sling. And that chicken basket has either to sit extremely well on her head or must be so stuffed that no chicken can move - otherwise, she'll need a hand to steady it occasionally.
Taking all this together, my guess is that we see a travelling situation plus spinning - maybe showing that a travelling artist's wife is a pretty normal female, except for her taste in men. I can also imagine that she spun, as usual, when possible during the travels, but maybe not packed like that and while on the move. However, we won't know until we try, and it would surely be fun to try and recreate that situation! Anybody got a medieval household and an ass?
*chuckle* I am short the baby, the ass and the distaff. I could pretty much manage to come up with the rest from my early 16th C kit...
I tend to lean toward the 'look at all the stuff it takes to travel!' idea. As for her spinning, of course she is; it takes a lot of thread/yarn to make clothes, points, laces, belts, bags, etc. etc. etc. *grin* It seems like almost all women were spinning pretty much any time their hands weren't full of some other task. One of my other favorite images is the one of the woman spinning next to the fire with a lit taper in her mouth. Now *that* took some skill!