If I was dedicated to not getting pregnant I would either get a bit OCD about taking the mini-pill (b/c you must take it at pretty much the same time every day - you have less than an hour window of difference before efficacy starts to drop) or else do the minipill + condoms or something like that (maybe spermicide).. I know quite a few people who got pregnant on it or ovulated while on it.
Given your daughter's age and eating habits I wouldn't count on the 'breastfeeding for birth control' as a second layer of protection anymore - that is most effective for babies under 6 months, who are nursing multiple times at night, and don't take any artificial nipples (no pacifiers) and aren't on solids. Once you start removing each of those variables the rate of ovulation and fertility return increase.
Mom of 4: Boy (10), Girl (7), Boy (4), Girl (2)