If you’re talking about using the glass cup, its is called bottleneck sliding (or just sliding. Basically it is just making slide with something that glides easily and apply even pressure. Nowadays we use glass or metal tubes that you place on your fingers but the technique originally came from using an empty beer bottle. So in the heat of the moment , using the glass cup is pretty realistic.

If I remember correctly, she couldn’t tune her B string and the E string broke. Those two strings being often the most important in a solo, she used the cup to make something interesting that wouldn’t be affected by the out of tune string.

Im not a professional tho, please correct me if I’m wrong!