O.K. let's try to make some sense in all of this.
First off, Mississippi retains jurisdiction on the immediatly scheduled hearing. IF that hearing results in a court order then the order will be valid and need to be domesticated in Texas or wherever you move.
Secondly, the mother has every right to file in Texas (although we still don't know what the issue of the filing will be) even if it's for a change of jurisdiction. By the time the hearing in Texas is brought, the conditions to sever jurisdiction from Mississippi will have been met.
That simply means that any future issues (if jurisdiction is transferred) will be heard in Texas. It does NOT mean that the hearing in Mississippi will be cancelled or even that it will become void.
Third, Since you (and hubby) moved from Mississippi (although we don't know the contents of the custody order) without permission of the court, mommy could easily file a show cause for contempt for moving the child out of the state holding jurisdiction.
It matters NOT where she moves. Hell, she could move to the moon for all the court cares. What matters is that the CHILD is controlled by the court order and, by proxy, you and hubby.
And lastly, get the language right. Hubby has a daughter. YOU do not (at least where this child is concerned).