Does she have a lot more experience training on the stationary bike? She’s standing on the stairclimber using all of her body weight so I’m not surprised that it’s higher. The RPE is interesting. Let me know if it’s a new modality for her. Also, is she measuring off of her own heart rate monitor or the machine’s? There may be some variability.
Is she safe at 160? Has she just started working out or has she been training vigorously all of her life? Does she have any pre-existing conditions? Does her doctor recommend any upper limits for her?
Nothing is black and white. Take a bird’s eye view of the entire picture.