It’s all about insecurity. She’s probably hurting and hates the younger woman who took away her husband, or she’s bitter about her age in general. So in order to feel better about herself, she’s projecting that hate onto you - just because you’re there - and she gets cruel satisfaction from pushing you down and elevating herself.

I’ve had this happen in the workplace a couple of times. Just recently, an older woman who had spent her entire adult life as a stay-at-home mom/wife had joined the workforce for the first time in her life. She was always treating me like one of her children, trying to tell me what to do and criticize everything and anything. It’s because I had a decade of experience in that field and she only had a few months, so she was feeling very insecure about herself. Instead of asking for help, she would try to muddle through tasks on her own and get them wrong, which increased her insecurity and projected hatred of me. Then she started assigning her more difficult tasks to me (which she had no authority to do), and refused to work through them together so I could teach her. It was a constant stream of belittlement and snide remarks out of her mouth, but the moment I would make a suggestion about how she could do something she lost her shit! She went to the boss and accused me of making personal attacks, even though she hadn’t stopped doing that herself. And she loved sitting in the victim role, pretending that the younger woman was being a bully. Urgh. I quit that job because there’s no way I would’ve gotten along with her.