Yes. The sewing machine is only drawing 0.4amps (400ma) so pretty much all solar "generators" (I hate that name) will provide that at their AC outlet. If they get a moderately expensive solar "generator" that will provide 10amps or more on the AC outlet they can use it for other things, like a TV, radio, or laptop charger, but 10a is not enough for heaters or hair dryers. Electric heat sucks down the battery power really fast though so I would not plug anything into a battery pack that makes too much heat.
Also make sure they get one with a proper cold weather cutoff. Freezing weather can damage some types of batteries. I think it damages LiFePo. Don't quote me on that.
The amp rating on an outlet is the MAX amps the outlet will provide before the outlet shuts off, or the fuze blows. The fuze is there because internal components are only rated for 10 amps and the manufacturer would rather have the fuze blow than have internal components blow.
