Cubans, please help me out with an etiquette question!?

She's Hispanic - she gave the gift out of her own good will, with no concept of creating a debt which you had to repay. If you wish to be similarly benevolent, then do so at another time, and in the same circumstances (i.e. that she owes nothing in return). It doesn't have to be anything tangible - you could invite her round for coffee and a snack (or whatever you feel comfortable with). If she sees him with the toy, that will be reward enough for her.