We can only go by what you’ve written which is quite brief. So without a back story, I think one call inside a week is very little in way of contact to ask for.
My DH is a very involved father, I’d be very concerned if he wasn’t speaking to his kids for a full week, wherever he was and whatever we’re doing. I mean on a honeymooon I’d rather he do it at a sensible scheduled time, rather than in the middle of our / the kids dinner.
Early on, DH would practically beg mum to let him FaceTime for 5 minutes on not-his-time and she would generally say no, they’re her kids it’s her time, hearing his voice makes her sick etc, but she would flip out if the phone wasn’t answered for FaceTime if they were with us (not maliciously ignoring, if the kids were in the bath or eating dinner) and we’d both get pages of rage text going on for hours about it, even if I wasn’t even home I’d still get it. But on the very rare, occasional time we were away - such as our honeymoon, or a friends wedding, she would insist FaceTime had to happen right now immediately or what sort of shit father is he. I have never forgiven her for sending multiple ‘emergency i need to speak to you urgently’ messages at a friends wedding, (she knew we were there as she’d asked last minute us to have the kids extra that day, but it was childfree and RSVPd months ahead) and it was just to ask ‘was it the orange or blue Doritos SK tried at your house and liked’. DH walked out thinking it was an emergency, and it was just that.
so I do know that sometimes there is more nuance than a simple ‘should DH FaceTime his daughter this week’ but ultimately yes, even if the mother is a nightmare (I’m not suggesting that’s the case for you, just that you mentioned it was mum asking not your SD) but the children are always innocent in this. And she is only 9. There should be 30 minutes at some point on your honeymoon where you’re busy washing your hair or not joined at the hip that he can make this work for everyone.