All banks have there own internal policies. Having someone put you on as an authorized user I think is helpful but only if they are super responsible and pay off their CC balances in full every month. You dont want to but an AU on accounts that are maxed out or behind in payments.
And some banks will not give you any favoritism if you are the AU - they disregard this as it is not your account.
Having your own primary accounts is a better way to go. And as to how many accounts constitute "suffiient credit history" that has very little importance - the AGE of the account is what they want. If person A has 5 accounts that are all 6 months old and Person B has 1 account that is 5 years old - Person B is a better candidate for better approval odds.
So I would accept her offer to be added as an AU if as I mentioned - she is a responsible borrower. And maybe if she really believes in you and wants to help you - maybe the most effective solution would be for her to co-sign for a new account - that way you would get credit as a primary holder and benefit from her stronger credit history. I would start with banks that are young history friendly - like Discover or Capital One.
Good Luck ! And keep us posted 
@Anonymous wrote:Also please tell me how many lines have to be on your credit, for you not to get the response "insufficient credit history"
Has nothing to do with how many cards you have. It has to do with how long you've had them.
