Welcome GravelGordon to HDTimeline. You will find a lot of information and fellow riders with similar interests and creative solutions to your questions. Browse the Self Help and Search tabs near the top of this page to find answers.
The most cost effective solution is to adjust the bike handlebars, hand & foot controls first. Common solution is to rotate bars towards her, so she does not have to reach so far forward. While holding the bike vertical, have her close her eyes and reach for the bars, palms down fingers extended. See where her finger tips touch the hand controls.
Next, have her do a two or three finger squeeze on each...if she has trouble pulling the levers to the grips, they are too far away or she may need an EZ clutch on the left and possibly different lever adjustment on the right. Her back should be fairly upright, and should not have to shift herself in the seat to reach. Do the same with the foot controls...do her heels lock on the peg and reach the gearshift and brake pedal at a relaxed angle with no cramping in the shin area...you have to remove the bolt and nut completely, and adjust the level/pedals a notch at a time up or down to suit.
If after all the above has been done, and you notice she had to shift around on the seat, a new seat is likely needed. Also, she could be fighting the wind, so she may want a Quick Release HD fairing. In either case, you are looking at $250 to $350 for each accessory, less $100 if buying used...but do the adjustments first...many times it is simply the easiest way to rider comfort without a lot of green.