Am I allowed to have a lady helper in my house with condition that my husband never see her? I know it's very hard to have one who can travel with Mahram but I'll do my best if Islam allows that she lives in my house without her Mahram at the same house. I have 6 small children and I'm in a real need.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
There is no harm in hiring a lady to help you in your housework if you will observe what you have mentioned, i.e. that your husband will never see her. In fact she should be veiled in an appropriate manner so that neither your husband nor any other man in your home could see her. Again you should make sure that she never stays alone in your house with your husband or any other man.
Look for a good Muslim woman.
As for your bringing her from her country to your home, we suggest one of the following:
1. Bring her husband with her to work with you or any of your neighbors.
2. Pay a ticket for one of her Mahrams to bring her to you and return to his country.
3. If you can not do any of the above we think you could bring her even without a Mahram as long as you are in dire need of her services.
Allah knows best.