While joint popping is not necessarily anything to worry about unless she seems to be in pain, it can never hurt to stretch a horse ^^
We also have a senior QH mare who has very minor artheritis, and although your mare is half the age of ours (she turns fifty in february!) I think that these exercises would help your gal just as much as ours.
I would advise in stretching her all over
and not just those popping joints, though!
This video has a lot of nonsense at the beginning. The girl seems rather...scatterbrained. That aside however, this is a VERY good demonstration of different exercises to do with your mare before riding. If I were you I'd just start the video at 1:10, which is where the information starts. We do all of these with Delriah, as well as a few others which I will also put up. forelimb stretch: hindlimb stretch:
And a favorite of ours for all of our horses: carrot stretches:
Also just a lot of circles, serpentines, slow jogs, and long and low walking can help warm a horse up before doing any loping or trotting.
Hope this helped a bit!