Need help with a family member - which is also our neighbor

Well, this is a very awkward situation - however, one that I believe, we may need help with. My Sister-in-law, husband (which passed away) and son moved here from out of state and upon her arrival offered to loan us the money for the property ($29k) we were/are living on - interest free. We surprisingly accepted and paid for the property with the loan (deed is in our name - no liens or mention of them on the paperwork). We have been paying back the loan for the past year and a half at $500 per month. Shortly after their arrival, they started to display vindictive behaviour towards my family - mostly being very competitive and hateful to my daughter in particular (she is a strong willed teenager). We decided to stay away and go on about our business. Today, my husband confronted her about an issue that happened over the weekend (she was drunk and phoned my daughter due to her son making statements about her) and she snapped telling my husband that her 12 year old kid complains about the way we treat him all of the time and that she wants her money now. We recently fell upon hard times and she offered to allow us to forego payments for a couple of months, which was great. Honestly, we have never yelled or treated him any differently from our own children - ever. We plan on paying her at the regular agreed amount of $500 per month, however, is there anything she can do to try and make us pay her in full now? She purchased the five acres next to us and built her home on it, she uses our driveway as enterance to her home/5 acres. I did not realize how much she resented us until today. My mother and father-in-law live on the other side of us. She has tried to turn their father against my husband, which did not work because he is a mutual person. The deed is 100% in our name and we drew up (on our own) a simple loan agreement, which was never notarized. If there is any insight you can provide, we sure would appreciate it. No one is innocent in this matter, however, I do not want to lose my home and property because she is an angry person and competitive with her brother/me. Some things are just too good to be true. My husband and I decided that if she tries to enforce legal matters, we will place the 35 acres up for sale, pay her off and then she can have herself a new neighbor - which means moving her driveway and putting up fences to seperate her property from the 35 acres. This has been going on for a year and a half. Imagine coming home everyday and having to deal with this woman that displays bad behaviour when she is drunk. Thanks, in advance, for your help.

If you have concerns about the legality of the agreement you've entered into, I believe it's in your best interests to have an attorney review the document to make sure. Unless the agreement calls for payment in full, based on failure to pay (for example,) or spells out any other circumstances, such as a balloon payment due at the end of a specified timeframe (again, just an example,) both parties are bound by the terms of the written agreement. One can't simply call a note "due" based on bad feelings or family disputes .. however, since you've already fallen behind, you do stand a good chance of her calling the note due based on your lack of repayment. (Hard to answer this well without reviewing the agreement in full.)
Again, I would recommend an attorney review both the note and the deed to make sure there are no hidden "loopholes" and that your interests are fully protected here. At any rate, I'd strongly suggest you resume making the scheduled payments as soon as possible, if you haven't already.
*You may also want to explore the feasibility of obtaining a shared driveway agreement if that one driveway is the only access to both of your properties.*
Good luck to you.