Why wont my 1 1/2 yr old sit long enough to eat? ?

My daughter just turned 1 1/2yrs and for the last few days she dosnt want to sit in her booster chair and eat... its not a high chair.. its the kind that gets strapped to our kitchen chair... I thought maybe taking off the tray part and letting her use the kitchen table would help but no it didn't... like this morn for instances I made her oatmeal.. of which she's had before nuttin new.. I licked her up and out her in her chair to eat and as soon as she sat she start whining... so I continued to try to feed her and she just flals her arms and turns her head from left to right and wont eat... so I took her out and tried to c if she'd eat running around and she did... but im not gonna chase her around the house to get her to eat... there's days she don't wanna eat dinner which means she goes to bed with no dinner and that bothers me.. how do I get her to sit and eat? Sometimes she will sit and eat but there's days she wont eat lunch or dinner... plz help