Steering effort can be changed but first one must know that the steering mechanism is OK. Is the power steering working as it should? Are the ball joints OK or worn, same with the idler arm and tie rods. There's a steering damper whose function is to stiffen the small steering movements and so absorb and prevent road vibration from being transmitted to the steering wheel. Any competent mechanic can check these items.
Then there's the front wheels' alignment which consists of the wheels' camber angle to the pavement 90 degrees less a fraction of a degree, their toe-in or parallelism to each other - about 1/8" closer together in the front than their trailing side and finally, the caster angle which is the difference between the wheel's top vs. lower pivot point. Think of a door on hinges, the lower hinge being NOT vertically (plumb line) below the upper. So? The caster angle is the effort she's turning against. The other side of that coin is that the caster angle helps to self center the car's steering to the straight ahead position. There are specifications for all these settings and those have a small range of allowable values: i.e. 10 degrees +/- 30' (that's 9.5 to 10.5 degrees). I suggest that if all the mechanical aspects are checked and found to be in order that the front wheels be aligned with a bias toward REDUCING the caster angle to its minimum allowable specification.
I found the steering of my '80 300SD to be needlessly heavy and that did the trick.
You should also know that under inflated tires cause heavy steering, try
28 to 30 psi in the front and 30 to 32 psi in the rear - that might sufficiently ease the effort to avoid the alignment adjustments.
If none of these solve the steering effort problem she should test drive a Honda, I believe these have very light low speed steering effort.