Raisins are not a magic ingredient that makes any dessert wonderful.
Like currants in Britain, used a lot traditionally. Even too much.
Soaked dried cranberries are a good alternative to raisins, soaked dried cherries too, although they're expensive.
The elderly Poish lady that the cake's for may have left Poland many many years ago in which case it wouldn't be nostalgic for her, however my favourite cake here is Wuzetka, a post-war creation invented in Warsaw to mark the opening of Trasa W-Z (the east-west highway).
Szarlotka or sernik are both good ideas, especially sernik.
If the lady's from eastern Poland, there's that very nice Easter Cake that's not baked (they make it in Ukraine too), however not everyone likes it. There's also babka, however (despite all the fancy recipes online) here. it's often something a bit like a madeira cake in a round mould.
Here's an OK sernik recipe. It's from America so they use cups (big ones? little ones?) however if the OP's from there, he/she will presumably know what sort of cup it is, otherwise it's possible to convert cups to grams or ounces on google.. There's also Krakow sernik, a bit flatter and slightly different. Both are good.