Bismihi ta'āla
The simple shar'i answer is no. The contract she enters into will not be valid. However, one must not look at this only from a shar'i side, but more from a moral and social aspect as well.
In general, it is Islamically wrong and very disloyal if one engages with relationships without knowledge and blessings of parents. If they disapprove, that is even worse.
And Allah knows best