Here is a more affordable idea...in case you are not sure she will be into it; just goes around jacket and provides grips
https://www.denniskirk.com/347291.sk...FfA-Mgod-TIAww
My other suggestion is to get her some cheap leather pants or something with more grip. Denim doesn't provide the best grip and that can really effect how well she can hold on; legs should be used to squeeze the bike and therefore require less arm strength....and don't forget women usually have powerful legs for their size so these should be utilized.