Oh, I just love
I have a friend like this - wonderful person and I love her, but if you mention anything about weight loss or nutrition, watch out! She will preach her personal gospel to you, though her methods (usually involving something radical, impractical, or faddish) don't even work for her!
When people start into conversations like that, I tend to change the topic as quickly as I can, or if I'm on the phone, I'll (politely) interrupt and say that I'm so sorry but I do need to go, if the topic-changing doesn't go as planned. It sounds like her heart is in the right place, trying to help you, but unsolicited advice can be a little annoying! People's experiences can leave pretty strong impressions in their minds, and it's saddening that one negative experience in the OR has turned into a sweeping generalization about the entire healthcare system.
You have a few different routes on this one, I guess. You could attempt to enlighten her that nurses are in general a smart, savvy, compassionate, intelligent bunch, but it might end up in a no-win argument. Being a non-confrontational person myself, I tend to avoid this option, though I know many people who can debate well and would be fine with this. The other option would be to simply nod and listen. If she's just ranting in general and not directing anything specifically at you, then let it roll off your back. Annoying, yes, but not anything to lose sleep over. Set boundaries and keep the conversations short if she seems to be stepping on the soapbox for too long (see above techniques). It's just really, really hard to change people! Perhaps once you are an RN, her opinion of nurses will soften a little, or maybe change to "nurses are incompetent except for my in-law StudentNY, now THERE's someone who has a clue..."
I tell people I'm pursuing nursing - I'm still doing my prereq's - and I inevitably will get a health question or two. On things I don't know, I just tell them that I haven't started clinicals yet, so I'm not sure, but I'm excited to learn about hernias/wheezing chests/strange infections/cataracts in the upcoming years. That usually works, along with a that-would-be-a-great-question-for-your-healthcare-provider deflection. Don't feel stupid because you don't know something you haven't learned yet!
And the "crazy for going into nursing" comments - I agree with Stressgal. Ask them why! There are ups and downs of every career field, and we all know that no profession is a perfect one. You can be someone to clarify some myths and explain your reasons for becoming an RN.