Some of them, sure.
Some of them aren't difficult at all, like Brokenhearted Girl and all of the stuff on Dangerously In Love.
I think her most vocally challenging songs are on B'day and 4.
Most of B'day is centered at the upper 4th - lower 5th octave, and if you don't have that stamina and control those songs can easily tire you out. The only songs that aren't that high on B'day are Kitty Kat and Upgrade U.