If you give us the type of car and any other equipment she already has we can be of more help. As has already been said, you can almost always find a way to get a 5.25 or 6.5 in a stock 4x6 spot, but the amount of work needed depends a lot on the car. Is she going to amp the speakers? Running subs? Any by "no budget" does that mean she's made of money, or she doesn't know what she wants to spend yet?