Your translation is right, except for ‘saw’, which should be ‘had seen’, since her seeing of the ornamenta precedes her wanting them for herself (cupiebat). I just checked and see that Lewis & Short does record the form MOENIIS as an ablative plural found in an inscription, but you’re right that it really should be moenibus here.
As I recall, these are done pretty well in terms of the grammar, but there are a few errors (which may have since been corrected, I don’t know). Here’s one that has stuck in my memory: