介词with能当主语吗?比如Linda with her mother __shopping now.is go are going is going are go主语是Linda with her mother 还是her mother

这是个主谓一致的问题：
主语是Linda, 不管with短语，动词与Linda匹配。
还有以下词组，也可以这样用：
“名词 + with, as much as, rather than, more than, no less than, as well as, such as, in addition to, with, along with, together with, except, besides, but, etc"
e.g. John, rather than his roommates, is to blame.
The ocean, as well as the gulf and the bay, provides good fishing.
John as well as you is wrong.
No one except two girls was late for dinner.

Linda，her mother 是主语

主语是Linda ,with her mother 是附加成分,句中有now,用进行时态,所以是 is going

Linda with her mother, is go 单数第三人称用IS