Mom came home, didn't throw her disposable mask in the garbage bin I placed at front door. Where was it?..on her bed contaminated side down.

Here is more information on Karen70's situation.
https://www.agingcare.com/questions/what-is-one-to-do-if-an-elderly-parent-refuses-to-go-get-tested-for-covid-464168.htm

If it helps you at all with the stress, we wear the same masks for a week in the hospital.. Both sides are probably contaminated. And we wear them out of the hospital and into our cars,,, and then again the next day

amen

Technically both sides are contaminated but that is beside the point.
Was this the first time this happened? If so ...she forgot. I would not make a big deal of it.
Spray the bedding down or change the bed
Might want to get washable masks and keep several on hand. Much more economical.

Spray her bed with lysol.....if shes not concerned, not much more you can do....

I'm not sure there is a question here, as it sounds more like a vent(which is fine too), but if you're concerned about her contaminated mask being on her bed, I guess you can always wash her bedding. Sometimes we have to pick our battles, and I'm not sure this one is worth it.