This is what the manager tried to distinguish by saying she could be outside but not inside the store I suppose.
Prairie
I think it would probably be legal within the store, too. It's just that most businesses don't want to associate themselves with a partisan political view. My registration table at the mall was on private property (commons area, not within a store) but the mall's policy was to allow registration tables for both parties.
The real problem with all this is states like CA that are utterly lax about validating the legality of voter registrations. The so-called "motor voter" law was a bald example of Democrat-inspired voter manipulation. It's designed to register illegal aliens, skulls full of mush and welfare types who would never register on their own but welcome government hand-outs. They register them as Democrats and pick them up by the bus-load to haul them to polling places on election day.
They also spend fortunes on "walking around money": cash payoffs to street people, etc. to get them to vote. They do everything but mark the ballot for them in the booth (they show them how beforehand!) Sadly, both parties do it but the Rats are way ahead of the Pubbies on this. They have multitudes of warm bodies from unions who are more than happy to spend a day compromising the Republic.