It sounds like Gerber's marketing strategies are adding to your anxiety.... You said your daughter "loses interest" after eating half a jar of baby food, but please realize, she is FULL. Little ones stop eating when they are full. It doesn't matter what size jar the baby food manufacturer is using, and whether your daughter eats half the jar or a third of the jar. If your gut tells you she should be eating more, consider giving her more frequent, smaller meals.
And don't get sucked into the Stage 1-2-3 phenomenon. My son was late to get teeth; I don't think his first one came through until he was 10 months old. My mom was trying to feed him Stage 3 foods because of his age, and she was getting impatient with me because I was still feeding him pureed foods. My son was gagging on them and not really doing well with the chunky stuff. By and large, my husband and I were not feeding him commercial baby food, we were just pureeing canned fruits & veggies in the blender, so I was sort of oblivious to the "Stages" issue.
I would keep feeding her pureed stuff for now, and give chunkier foods a try in a month or two. I would also take a stab at making your own baby food. With a blender, you can experiment with textures between "pureed" and "chunky", and see how your daughter does. You don't have to do any fancy recipes; all we ever did was buy canned fruits and vegetables.
Good luck!