Please don't push her on it, the hello and goodbye in particular. It's very very common, at this age and even up to 4 (4+ sometimes). It's no reflection on her manners or your manners or anything. If you try to get her to "overcome" it, it might well prolongue it and/or make her hypersensitive about it.
The thank you element, I would just say "We say "thank you", don't we?" as a reminder to her when thanks is necessary, (and see if she says "Thanks", (if not then at least you have brought the "thanks" up at the appropriate time, she will do it herself in time, rather than forcing her to say it or not acknowledging the appropriate moment for a thank-you) or, "What do we say? We say "thank you".. Thank you, Grandma!". (ie model it for her).
The Hello and Goodbye, I would always invite her to say hello/goodbye, but if she doesn't, I would just leave it. If she won't say goodbye, you could invite her to wave at the window, but even if that's too much then I would just not push that either. If you feel it looks like she's being rude, explain to whoever it is (if you feel so inclined) that she isn't very keen on hello and goodbye, but she isn't being deliberately rude, it's a common thing for children her age and pushing her on it is counter-effective, long-term.
I know it feels distressing when it seems as though manners are not being observed, but you need to overcome your own discomfort (if any) that she doesn't say it because it really is an age thing and very common, and pushing the matter will only be stressful for both of you, and probably will not result in her saying it naturally anyway.