I have seen some people who apparently apply again and get it, quite how often this happens I have no idea, I doubt it is that common but they only have the application fee at risk.
I remember entering the US and was asked how much I had on me, less than $20 in USD but like everyone else I had CCs.
Begs the question how many people visiting the US do not have Bank Accounts, must be very few.
How is a Bank Account proof of a tie?
Enough depends on their plans as mentioned above.
From a practical point of view I assume she is not in a position to increase her balance anyway, it is what it is.
Review the questions asked in the DS 160
Vacationing in the US is not cheap, the airfare will be substantial, I suppose a lot will depend on her plans, how long she will be staying, what she wants to do, sort of places she likes staying etc etc.