If I read your post correctly, she's peeing rather than leaking. The Proin won't do much about that, although it may control the leaking enough so that she pees, if you catch my drift.
Since she's picked out two spots, and you're not worried about one of them, I'd be inclined to find something to cover the bed. I use washable human incontinence bed covers. They're about 2' X 3'. Or you can use baby mattress covers. If they don't stay in place, just wrap bed and covers in a sheet. When she pees, you need only change the sheet and covers.
As KF_in_Georgia said, there may be problems if the other dogs share the beds and track through it or (ahem, Poppy) cover it.