20 month old eating issues

My toddler has generally been a good eater - good portions and sits at her high chair fine. But the last three or four days she’s refusing to sit to eat, or eat at all. She’s really not eating any meals at the moment, she eats breakfast ok and then a few snacks in the morning before her nap but won’t eat anything for lunch or dinner and is just not interested and just wants to run about. She’s quite small anyway and I am worried about her weight. She may be teething but I can see her last ones have cut through - so I’m not sure if it’s that. Has anyone else experienced similar at all? I’m hoping it’s just a phase and my mind can put to rest