Would you entrust her to share a cabin with a complete stranger for the week or however long the trip would be?

She would want her own room, but be able to eat/tour etc. with a small group

You can look into Road Scholar, they organize groups for cruises.

On most cruise ships, unless you find a one person cabin (NCL offers them), there is a thing called "single supplement" where effectively you are paying for 2 people but only occupy by one person. Your cost of crusing is essentially doubled. You are better off to find her a companion (a grand child, perhaps?)

There are a few travel agencies that specialize putting together senior groups. Eldertreks, Senior Women’s Travel (SWT) came to mind. You can google them and look over their web pages.

Since I have not used them myself, I cannot offer any comments on how good they are from a personal perspective. I have friends who had booked with them and the comments were generally positive. I also don't know if they organize crusie groups but I suspect they would.

One thing you may consider is that many local travel agents offers "escorted" tours. There is a tour guide that travels with the group and organize everything. The traveller essentially travelled by themselves, but they are part of a group where they will travel together.

DW and I are "wanderers" as we like to do our own things. But we did joined a couple of escorted tours for the convience factors, especially for travelling to far off places where language abnd customs are issues.

And more than likely, if we see the right "escorted tour" comes along, we will not hesitate to book.