My colleague is very hard on me since her granddaughter has come to work?

My colleague is about to retire, but she says she needs some work to do, and she brings in her granddaughter to work. But since her granddaughter started work, her grandma was very hard on me. Whenever I am doing my work, she is always behind my back watching. Whenever I am not in the office, she would talk to other colleagues how awful I treat her. I did not treat her badly. In fact, i always praise her granddaughter. Once I was on computer filling in some professional development forms, and I emailed it to the school and get sent another email via my personal email address, she complained that I was reading my email at work times. She is pretty awful....I don't know what to do with her. She says her granddaughter gets evaluated on her first day of work, and the boss asked my colleague (grandma) to grawl at everybody whenever the boss was not around, even though we have done nothing wrong. But grandma likes to complain about me all the time. Basically she did nothing but to watch every one in the office, especially me. She says I wasn't nice to her granddaughter since she starts work, and I think she is an absolute bitxx just to irritate me...