Alexis, ok, here we go so buckle up..

Can you give me a bit more information or anything you may have, the religion of your ancestor(s), the approximate year of arrival of your grandmother, a scan if you can upload of the main page of her passport, France can be difficult depending upon the year being researched and names as dilalect really plays into things. As of now, here is what the LDS lists on their data base for online recores for a soundex search of "Pin, France"
Badecon-le-Pin
France, Indre, Badecon-le-Pin
Bailleau-le-Pin
France, Eure-et-Loir, Bailleau-le-Pin
Beaumotte-lès-Pin
France, Haute-Saône, Beaumotte-lès-Pin
Brette-les-Pins
France, Sarthe, Brette-les-Pins
Chambornay-lès-Pin
France, Haute-Saône, Chambornay-lès-Pin
Cléré-les-Pins
France, Indre-et-Loire, Cléré-les-Pins
Cuges-les-Pins
France, Bouches-du-Rhône, Cuges-les-Pins
Eyzin-Pinet
France, Isère, Eyzin-Pinet
Fontaine-le-Pin
France, Calvados, Fontaine-le-Pin
La Breille-les-Pins
France, Maine-et-Loire, La Breille-les-Pins
La Tour-du-Pin
France, Isère, La Tour-du-Pin
Le Pin
France, Calvados, Le Pin
France, Charente-Maritime, Le Pin
France, Gard, Le Pin
France, Gers, Le Pin
France, Indre, Le Pin
France, Isère, Le Pin
France, Jura, Le Pin
France, Lot-et-Garonne, Le Pin
France, Seine-et-Marne, Le Pin
Le Pin-Murelet
France, Haute-Garonne, Le Pin-Murelet
Le Pin-Saint-Denis
France, Charente-Maritime, Le Pin-Saint-Denis
Le Pin-au-Haras
France, Orne, Le Pin-au-Haras
Le Pin-en-Mauges
France, Maine-et-Loire, Le Pin-en-Mauges
Le Pin-la-Garenne
France, Orne, Le Pin-la-Garenne
Le Pinier
France, Charente-Maritime, Le Pinier
Les Pineaux
France, Vendée, Les Pineaux
Les Pins
France, Indre-et-Loire, Les Pins
Les Pinthières
France, Eure-et-Loir, Les Pinthières
Mont-Pinchon
France, Eure, Mont-Pinchon
Nonant-le-Pin
France, Orne, Nonant-le-Pin
Parçay-les-Pins
France, Maine-et-Loire, Parçay-les-Pins
Pin
France, Haute-Saône, Pin
Pin-Balma
France, Haute-Garonne, Pin-Balma
Pinas
France, Hautes-Pyrénées, Pinas
Pincé
France, Sarthe, Pincé
Pindray
France, Vienne, Pindray
Pindères
France, Lot-et-Garonne, Pindères
Pinel-Hauterive
France, Lot-et-Garonne, Pinel-Hauterive
Pinet
France, Hérault, Pinet
Pineuilh
France, Gironde, Pineuilh
Piney
France, Aube, Piney
Pingon
France, Savoie, Pingon
Pinon
France, Aisne, Pinon
Pins-Justaret
France, Haute-Garonne, Pins-Justaret
Pinsaguel
France, Haute-Garonne, Pinsaguel
Pinsot
France, Isère, Pinsot
Pintac
France, Hautes-Pyrénées, Pintac
Pinterville
France, Eure, Pinterville
Pintheville
France, Meuse, Pintheville
Roquefort-les-Pins
France, Alpes-Maritimes, Roquefort-les-Pins
Saint-Barthélemy-le-Pin
France, Ardèche, Saint-Barthélemy-le-Pin
Saint-Denis-du-Pin
France, Charente-Maritime, Saint-Denis-du-Pin
Saint-Germain-du-Pinel
France, Ille-et-Vilaine, Saint-Germain-du-Pinel
Saint-Jacut-les-Pins
France, Morbihan, Saint-Jacut-les-Pins
Saint-Jean-du-Pin
France, Gard, Saint-Jean-du-Pin
Saint-Martin-le-Pin
France, Dordogne, Saint-Martin-le-Pin
Saint-Ouen-le-Pin
France, Calvados, Saint-Ouen-le-Pin
Thorée-les-Pins
France, Sarthe, Thorée-les-Pins
Villebois-les-Pins
France, Drôme, Villebois-les-Pins
Vorges-les-Pins
France, Doubs, Vorges-les-Pins
You need to determine a bit more information before you undertake even writing to the regional archives and be aware, France can be confusing, they have three main tiers of local administration: the commune, department and region. Unless you are positive about the spelling and region, sending letters in my most humble opinion will not help much at this point. Also, keep in mind with so many many wars, especially WWI and WWII, things changed, names changed, spellings etc. And, what was the port of departure, Cherbourg, France, Le Havre, France, Antwerp, Belgium or one of the ports in Germany? All these pieces help to find what you are seeking believe it or not.
If you so desire, you can go to this link and click on each and every name to try and determine if something fits the data you have, from there, you can move a bit more forward
https://www.familysearch.org/eng/library/fhlcatalog/supermainframeset.asp?display=localityhitlist&columns=*%2C0%2C0&PLACE=Pin&PARTOF=France&prePLACE=Pin&prePARTOF=France
Upload a copy of the passport main page, I will be more than happy to assist if I can.