It seems to me you will be over-scoping this rifle at 20X. What max range does your wife shoot? if it's 500 yds or less, I recommend you drop down to 10-12X on the high end. Even at 1,000 yds, I think that 14X is enough magnification, unless your wife has vision problems like astigmatism. Going to higher magnification will sacrifice field of view and increase glare (reduce contrast).
At 10X, a 40 mm objective is viable for big game. A 40 mm scope will be lighter and more affordable than 50 mm, and it will be bright enough if the glass is decent.
Pentax scopes have bad glare. In addition to Weaver, I would look at Burris Fullfield II or E1 scopes in that price range.
If she is a longer range shooter, then you should increase your budget and look at other brands. At 20X the Pentax will have poor contrast in critical lighting conditions, like morning and afternoon.