Re: advice & encouragement please!
Mama, I don't think you should be so hard on yourself about weaning your firstborn at 15 months. That's so much longer than most kids are nursed for, and while I think breastmilk is fabulous, it's not a miracle cure-all. Even breastfed babies get colds and ear infections and even asthma. So don't beat yourself up for only nursing longer than most women ever even consider doing, okay?
I think you are right to be concerned about how your younger child will handle you and your breasts being out of commission. I would nurse her right before surgery (if that is an option), and discuss what is to come with her several times before it comes to pass. "Honey, Mama needs to go to the doctor so the doctor can fix her tummy. I won't be able to nurse you while my tummy is getting fixed. But as soon as it's better, we'll nurse, okay?" You might be surprised how well that sinks in to a little brain!
I don't know that you should worry at all about your child slipping down the weight percentiles so long as she continues to grow lengthwise, meets her milestones, and seems to have plenty of energy. Some (incredibly lucky) people are just destined to be slender for their height! But if you are concerned about your daughter's weight, you might want to concentrate on feeding her more high-calorie but still healthy solids- things like whole milk yogurt and avocado, and olive oil, which goes nicely on/in a lot of things!
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"