This is the 9712th most frequent Russian word.
швейной
Sewing.
In this context, 'швейная' again modifies the noun 'машинка', denoting its function is related to sewing.
У нас дома есть старая швейная машинка.
We have an old sewing machine at home.
The word 'швейной' is an adjective describing the workshop, indicating it specializes in sewing or tailoring.
Она работает в швейной мастерской.
She works in a tailoring workshop.
Here, 'швейной' describes the machine, specifying its purpose for sewing.