Esmeralda,
First of all your English was just fine and your post was easy to read and understand.
Before you even mentioned your appearance I was thinking to myself that this "Sister" you mentioned, is probably a bit intimidated by you because you are well put together and have an education. You are the new girl in town and she may see you as somewhat of a threat to herself and her daughters. I'm also wondering if her Son may have thought more of your casual friendship than you may realize and he may have said something about his interest in you, to his Mother. Even though you have no intentions towards him, she may be worried about her Son becoming "unevenly yolked" with someone who hasn't established herself as a full fledged JW yet.
People are people and JW's are no different than anyone else, they just think they are. You'll meet women like this no matter where you go. It's just a bit more hurtful when it happens in a place where you've let your guard down and may have let yourself become more trusting because you've been led to believe that they are more trustworthy. Sometimes JW's are resentful of the attention new ones get when they first come in to the congregation. I think they feel a little bit like the prodigal son who stayed behind at home and did what he was supposed to while his brother went off and did what he wanted. To them, you have been living it up out in the big bad world and have gotten to do things they weren't allowed to, such as getting a college education. Now you show up in "their world" on "their turf" and you are getting attention for doing what they've been doing all along.
I don't want to discourage you from studying with JW's if you think there's something you can gain from doing so but I would recommend that you verify everything they teach you, from outside sources and not be taken in by the seemingly trustworthy way they have. Many of those you will meet are unaware that they themselves don't have the full picture when it comes to the origins of their religion and it's doctrines yet they really believe it and are only too happy to pass it along to you and expect you to buy into it 100% as well. They will also be suspicious of you if you question it or don't go along with it entirely. They only tolerate questions up to a certain point. After that, their radar goes up and they will be watchful of you.
Much of the behavior of JW's is shaped by unwritten/unspoken rules or ethics that they have developed themselves and are not necessarily Bible based. As with any tight knit group, you'll have to navigate your way through that until you either learn to conform to their ways or get simply get used to being looked at with sideways glaces. It can be done so long as you are aware of what is going on and can manage to avoid losing yourself in the process. Remember, you are there to validate them and their chosen path. Every new one that comes in and accepts the faith is a reassurance to them that they are on the right track themselves. Questions you may pose are a reminder of the doubts they may have suppressed for so long they've forgotten about them.