That sounds like a textbook wattage floor problem. You’ll need to list the trainer type for more info.
What FTP setting was used for the ramp test? If it was set to a really low wattage to begin with I can’t imagine the 6% ramps would be very noticeable.
At the end of the day I don’t think it’ll matter much as long as she keeps turning the pedals. At 58 watts 120% VO2 work is going to be under a 12 watt bump. Not a huge difference by any means.
I wish I could get my wife on a bike. It’s too hard to go for a jog together with a little one in tow.