My child is not talking normally after having her tonsils out last week?

Her throat hurts. It is a full two week recovery from a tonsillectomy. Having them tonsils out will improve her health overall over the next few months. In the meantime her throat will hurt as it heals and that will affect her talking. If it continues, mention it to your ENT on follow-up which is usually at the two week mark.
Space management. Please start by taking her back to the surgeon who took her tonsils out. One of the things that determines the sound of the voice is how much space the soundwaves have to bounce around in before they exit the mouth. With the tonsils gone, she ought to have more room so things can sound off. Is she having leakage of air from the nose when speaking? This can be vpi- velopharyngeal insufficiency.