For my wifes lighter weight bow should I use 4" feathers instead of the 5" ones I use on mine?  Just want to put the same effort into her arrows that I do mine and not just give her something because I have it.

I don't think the weight of the bow matters so much as the amount of correction needed in the flight of the arrow.  With a centershot bow, target points, and well tuned arrows, you don't really need any feathers at all.  My 60# bow shoots bare shafts fine out to 30-40 yards, if I have a perfect release.  Considering that I don't always have a perfect release, feathers are a nice thing to have on the arrow.

On the other hand, move the arrow out from centershot as with many longbows, shoot broadheads that will catch the wind, and have less than perfectly tuned arrows, and you may well need 5" or longer feathers.

Short answer: if she is shooting a recurve cut close to centershot, you've tuned the arrows to the bow, with target points, 4" feathers should do fine.

You can go smaller if you wish if she is shooting carbon or aluminum shafts.4" is overkill on some of the small diameter arrows that would shoot from bows that weight.jmo

my wife shoots 3D's and targets with field points only. she doesn't hunt or shoot broadheads at all. i agree with mcdave, poundage doesn't matter. she shoots carbon arrows with 3" shield cut, 3 fletch. she has shot in cross winds so her setup for her shooting has enough stability and her tune is good. she has even shot with me in the rain. and her arrows fly good.