I am trying to help my Mother-in-Law plan for a broken chain... not one split intentionally
Oh! I see!
My inclination is to give her a connex link.... she can use her chain tool to pop out two adjacent rivets by the break, and connect the inner "ends" with a connex link...In that case the replacement shimano pins might be unecessary?
Yes, Neil, I think you can dispense with the Shimano pins in that case, as they would add unnecessary hassle for her.
You might see if you could get 'hold of a three-pack of connecting links to cover any eventuality by these same means. It is easy in field conditions to drop or lose a link half). That way, she would have a bit more margin (and sometimes there are specials on 3-packs, as there were for my most recently purchased KMC connecting-links, totaling about $USD9 vs. the same price for a single SRAM if I hadn't had a special coupon to spend on it, which dropped the price to $6.95 for one; the KMCs and SRAMs have worked identically on my Shimano 9-sp chain. My spare Shimano pins are still in their original packaging, unused).
I think your plan for her is a good one. There really is no harm in running multiple connecting links on the chain (again, so long as all are compatible with the same-width chain).
Good on you for helping her so ably; I'm sure she's very proud of you, and you can stand a little taller for the effort -- well done!
All the best,