Why don't you say you're trying to lose weight and eating smaller portions? No need to mention the jab. Or does she get weird about weight loss efforts?
I'm a little bit worried as I'll be going abroad with different foods etc, out of my usual routine, and do wonder how people will react to me saying no to things, like 'what do you mean you aren't having dessert?'
But on the plus side plenty of time to be active outdoors so fingers crossed.