Weaning and quantities?

Am taking my daughter off jars as she's now 12 months, at the moment she eats a full jar for one meal a day (other she has what we're having) but my question is this: she's just ate a quarter of a sandwich, how much is this in relation to a jar? More or less? She doesn't seem interested in eating anothing much more than picking at a couple of her baby 'crisps' and I'm going to give her a yoghurt in 5 mins or so...do you think it sounds like she's had enough to eat??