Is repentance for negligence in prayer sufficient for someone who was not committed to prayer seven years ago, or must she pronounce the Two Testimonies and perform ghusl?

Praise be to Allah for your repentance and steadfastness. Allah's mercy is vast, and He accepts sincere repentance. Allah Almighty says: "Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.'" You were not required to renew your Islam or perform ghusl, because abandoning prayer is not an act of disbelief that expels one from the faith, even though it is a grave sin. You are required to make up all the prayers you missed since puberty. If you do not know their exact number, then make up what suffices to achieve certainty or strong presumption of discharging your obligation. This is the view of the majority of scholars and is the more cautious approach.