Maybe point out to them "jokingly" in a call that you talk to her every waking minute unless you're talking to them on the phone
Is this person your MIL by any chance? Lol
Maybe a bit of both, insinuating but in an advisory way? If they’ve never seen you talking to her (if you’re usually sat apart or on your phone) I can see how they might - wrongly- jump to that conclusion. Also, in another way I wonder if they might enjoy seeing you interacting with your child? My sister recently became a mum and it’s lovely seeing her with her baby and seeing her in a different light. But you obviously shouldn’t be expected to ‘perform’ for people! If it’s bothering you just mention it, doesn’t have to be a big thing. You might find it is from their own insecurity which would be much less annoying (!)
I’d just keep saying “we do” and that’s it. And I agree with @Steph that’s probably why she’s saying that and not to take it personally. A lot of people have unwarranted advice/opinions and sometimes you’ve just got to ignore it because you know it’s not the truth and even they probably know from you saying “we do” could even say “we do at home”. And if the person is generally too much, I’d limit the amount of time spent with that person.
I tend to find when people bring stuff up like this repeatedly it comes from their own insecurities about things they feel they did wrong with their own kids. I wouldn't take it too personally.