"make sure she stays" - you simply cannot make sure of this - free will, no slavery and all of that. If you would like to find a helper who is happy to continue working for you long term, plenty of good advice above. Interview well and check references diligently, treat her well and be considerate of her needs. Nearly all the helpers I've heard of bailing after a short time live in a dingy little room with no AC, internet access or other "conveniences" that are common and enjoyed by others in the home and work well over 12 hour days for minimum wage - under those circumstances they have little to lose by trying again...