I believe 1 size difference = 1/3", so 1/2 size difference = 1/6" - less than 1/4"
In any event, many people think the optimum size has relatively little to do with the boot length, and more to do with your foot length, in particular with the length from your heel to the ball of your foot.
Does anyone understand why Jubilee blade would be much slower than Matrix Legacy?
Based on
http://www.skate-buys.com/jufiskbl.html http://www.discountskatewear.com/p-409-ultima-legacy-blade.aspx?it appears that the Jubilee had a 3/4" hollow (unless the skate technician changed that) instead of 7/16" for the Legacy - so it effectively wasn't very sharp, which might mean she was skidding sideways a bit and wasting a bit of energy. If she wasn't skidding sideways, a 3/4" hollow should be faster than a 7/16" hollow.
Also, the Jubilee toe pick is pretty minimal and hard to reach, so it was harder to do tricks that use the toe pick, but unless she is now pushing with her toe (not good, according to the artistic standards of figure skating), that shouldn't matter - if anything, she should have been able to use a little more length of the old blades for speed.
The rocker was a little shorter (7' instead of 8'), which means it was theoretically a little bit slower, but not dramatically so.
It's harder for a "level 1 blade" to stay sharp, because of the material, and it might have rusted easily, but the o.p. says it was kept sharp (within the limits of a 3/4" hollow?), so I don't see those as issues.
The new Matrix blade is lighter, but for a relative newbie, it's hard to believe that is overwhelmingly important.
So, can anyone figure out why the old blade would have been noticeably slower?
Maybe it was really the old boot - that was less stiff, and the energy was wasted bending the boot?
I just don't get it.