First of all, 19lbs at 14mos isn't anything to worry about unless she is dropping weight. So long as she has been more or less consistent on the growth charts, I wouldn't get concerned. Dd was 16lbs at 1yr, and didn't hit 20lbs until 20mos, and now at 2yrs is only 22lbs, but she stayed more or less steady at the 5th %ile, so that's just her.
IMO, kids learn very quickly that mom is willing to make 4 different things to make them happy, and they use that to their advantage. 14mos is kind of tough as they can't express a preference for something before you prepare it, but I would scale back and start offering a meal with one or two alternatives (as in a different kind of fruit, not a whole different meal). They will eat when hungry.
Starting at about 14mos, I would prepare kid-friendly stuff dd liked for breakfast and lunch, and then serve her what dh and I had for dinner. Dinner always included something she had had and eaten before (even if she chose not to eat it that night). She was never much for bedtime milk, so we would offer a bedtime yogurt snack, but beyond that, we did not offer alternatives at dinner. Sometimes she didn't eat, but I usually found she made up for it at breakfast the next morning.
Personally, I wouldn't introduce formula at this point, particularly if she's had some milk sensitivities. You can ask your doctor whether vitamin supplements would be appropriate in her case. Meanwhile, keep offering a well-balanced diet, and sooner or later, she'll eat it. You might also try some fun new stuff, star-shaped or string cheese, graham crackers with cream cheese and a dollop of jelly, sandwiches cut out with a cookie cutter, etc. As far as fruits and veggies go, we had to offer many 20-30 times before she ate them. We'd put it on her plate with no pressure to eat it, and then eat the same things ourselves for dinner. A few months ago she wouldn't touch broccoli, but now she begs for it for a snack, raw from the fridge.