I don't think you should force yourself to hang out with someone who makes you uncomfortable. At the same time, I would probably devote more time to finding out exactly why she is uncomfortable with NIP - if it's a conversation about her, and reasonably respectful, it might get her thinking about her assumptions about women's bodies and where those assumptions come from. If you approach it from an angle of "We have really different views on this, and I'd like to understand your perspective more" she might be receptive to at least a conversation about it from her side.
What it will come down to, I would expect, is that she feels that a woman's breasts are essentially a private part, to be seen only by her husband and herself - and that modesty is more important to her than her ability to feed her child wherever and whenever. Her objections to YOU NIP'ing are likely to be along those lines too - that you are visibly demonstrating a different morality than she holds, and she's uncomfortable being friends with someone like that. But it's likely she's never *really* thought about it - everyone else says it's nasty, so she just agrees. It's unlikely that she will change her mind about anything, but she may end up realizing that what's right for her isn't necessarily what's right for everyone and might, just MIGHT, start thinking about where her values come from.
In the meantime, I know it's hard, but try to internalize the fact that you're in the right, here, legally (I think? Dunno about US laws.) If someone hassles you about bf'ing, as long as you're not in someone else's private residence, you can calmly tell them that you're not moving, and covering your baby will result in a screaming fit decidedly less pleasant than a quiet, happy, nursing baby. And that they are under no obligation to look at you. If you're in your mom's or your friend's house, unfortunately they do have every right to ask that you nurse elsewhere, but in a public place - including stores, restaurants, parks, churches, etc. - you can nurse where you like. Print out a copy of your state's bfing laws and keep it with you.