And, she's really introverted, so like yours, she's not very expressive, unless you cultivate a moment with her, engage her for a bit, and then, what's inside her head/her thoughts, finally appear.
This sounds exactly like my mother as well. She is VERY VERY VERY introverted. I once asked why she doesn't go out more and be social, and she was like "I just find being with people so exhausting. If I never had to go to a social gathering again, I wouldn't. I enjoy myself so much more when I'm reading, watching TV, surfing the web, walking my dog, or gardening."
She has really strong convictions, but she only shares them with those closest to her (me, her sister, and some times her parents). She was pretty liberal growing up in the hippie era. She was all about environmentalism and social welfare. However, she became a lot more economically conservative since joining the workforce 30 years ago. She is completely against public health care, and she doesn't think that the rich should have higher taxes or anything like that. She has a soft side for the downtrodden though still. She invests a decent amount of money into charities for children, especially around Christmas time. She won't donate to charities at the cash register though; she finds those kinds of requests intrusive and obnoxious. She's also pretty passive aggressive and into subtle guilt tripping whenever I do something that doesn't meet her expectations. I think Fi is evident in a lot of these beliefs.
As far as her Si goes, you can tell that it's a function that has developed for her later in life. She used to be a lot more free-spirited and optimistic about change. Now she easily gets stuck in ruts and is afraid to do anything that goes against her ruttish routine. She talks about change like she wants to pursue it, but I know that she's pretty afraid of it. She's not very detail-oriented, but I think her ability to pay attention to the details has heightened through the years. She is also leagues better than me at remembering where she's left things and sticking to plans (there's some Te showing through with that).
Her Te is also fairly developed. She was once very disorganized with her external world, but she has learned how to handle her money effectively, she files away important documents, and she has certain places in the house meant for certain items so she can better keep track of things. She also is a lot better at getting shit done than when she was growing up.
Again, she is very very introverted, so I don't see her Ne too much. I can tell she appreciates Ne very much though. She laughs at Ne-based humor, and if you get in a heated discussion with her, it's evident that she uses Ne connections to support her claims (even if I do find them "irrational" at times).
I get along with her fairly well, so long as we don't talk about politics. I just can't empathize with her arbitrary convictions. She is really into the green movement, and while I see the benefits of living "greener", I don't really attempt to live by "green" standards the way she does. I also just don't really give a shit if people are "rude" or go against my beliefs/expectations the way that she cares.
When I was growing up, she was a bit protective, but when it really came down to it, she pretty much let me do whatever I wanted, so long as it wasn't immediately life-threatening. She also values fueling her intellect and she can really get going on an abstract argument, so we get along well in that light. And she understands and empathizes with my flakiness, so if I am forgetful, unorganized, and/or irresponsible about some things, she doesn't really get upset with me for it. She's pretty open-minded for the most part (and when she's upset about something, she really doesn't let you know and just kind of keeps it to herself...very passive), but there are these minor things that she's pretty nit-picky about. For the most part, she's living in her head and doesn't care too much about jumping out of her head and landing in the real world.