Hi stack,
Your base layers (3" of 32 ILD and 2" of unknown ILD) may already be firm enough as a base layer. Thinner layers will “act” firmer because they get firmer with compression faster than thicker layers. If you were to add even firmer latex underneath this it would become softer because the foam you add would be softer than the floor. It would also have a wider range of compression and could be more adaptable to different sleeping positions or weights (see post #14 here).
Do you know the type or ILD of the 2" Talalay layer you have (and whether it’s actually Talalay or whether it’s softer or firmer than the 32 ILD)?
If it’s softer than the 32 then along with the 4" of “Walmart stuff” the upper layers could be too thick/soft which could be the cause of her back ache.
Yes … it’s always interesting to see how different people react to different combinations. Both of these would probably improve things and put her closer to the “support” layers which can improve alignment compared to the 4" of memory foam/polyfoam you have (which are probably fairly soft) but again it would depend to some degree on the firmness of the next layer down as well.
Phoenix