Lucky for your wife, and you.
If the rodent had jumped into her front wheel, it would have been bad for all parties concerned. Your wife most likley would have done a superwoman over the bars, the tree rat would have gotten shredded in the spokes, and you would have had to clean squirrel guts out of the spokes.
I also had that happen, fuzzy little bastard jump between front and back wheel, I looked down in time to see it going under the back tire.