The above comments have a lot of great points. As Nancy stated, each piece of equipment might measure differently. One thing I didn’t see, might have missed it, is if she takes any medications, or if she drinks caffeinated beverages, and/or if she was tired.
All of those can increase HR.
The other comments about the stair-climber taking more energy is true too. A recumbent bicycle is quite easier then the stair-climber.
Also, the more familiar someone is, from a motor memory standpoint, the more likely it is to be easier. Of course that varies based on the intensity…
Hope that helps,