Dog getting fussy with food

[CQ]

DDog1, nearly 8 yrs, is being really off with her food lately.

She's always been pretty disinterested in food but will usually eat what I put in front of her if she's hungry enough and there's nothing better to do - sniffing under the shed for mice, watching squirrels etc. I feed JWB kibble which is a pretty good quality food I think?

Over the last couple of weeks she has been ignoring her breakfast entirely, but guarding it quite aggressively from my other dog - a lab type who is of course completely food-focussed. After about 10 minutes if she's not eating it, I take it away otherwise greedyguts will eat it.

In the evening she looks disdainfully at her bowl, ignores it until DDog2 has just about finished hers, then hauls herself over and starts to daintily pick at it. Clearly sending me hate vibes that it's just not good enough.

I really don't want to have to start feeding her something different to the other dog. Nor am I keen on having to mix in something else to tempt her. I never indulged my children with fussy fads, and I'm really reluctant to start this with my dog who is becoming a princess!

I've checked her teeth and mouth and nothing seems to be going on there, her poos are normal and so far she's not losing weight although I'm sure she will start to as she's only eating about 2/3 of what she should have. Up to date with wormers etc

She will, of course, happily eat horse shit and any other revolting thing she can find on her daily walk. But premium dog food? Oh no thanks.

Any ideas? Anyone else had this?