What machine has she been using for sewing purses? These machines were not really made for sewing leather or extremely thick stuff on a regular basis. Sometimes you can get away with it for a bit if it fits under the needle.
Some use penetrating oil to loosen things up, but then one needs to use regular sewing machine oil. I would also suggest only using
sewing machine oil to clean the outside of the machine. See also
How to Clean Up and use a vintage sewing machine - videos by Muv and Fav
I'm thinking that it may be a machine actually made by National. I'm fairly certain that it was made to use a different needle system than what is available today for machines. It is possible (or so I've read
) that if you drop the needle a bit that it will work. Or if you put in "
15x1 rather than 20x1 needles " in a search engine there is another way to use more common needles.