She probably shouldn't have said that because while it's true that breastfeeding can delay O it's not advised to just rely on it, especially if you DON'T want to conceive straight away. Every time I was told not to rely on it.

You will usually O before you get your first AF so you may not be looking out for the signs you are fertile.

I've fully b/f all 3 of my bubs and the earliest AF returned was 10 months. I still used condoms if I wasn't sure ie had some suspect CM or had a twinge that could be O pain.