is a lot of vegetable oil bad for you?

Oils, even vegetable oils, are calorie dense and you're getting a lot of extra calories.... However, most vergetable oils are monosaturates and as such are reasonably healthy otherwise; they don't tend to promote cholesterol formation and some, like olive oil, may actually be protective.

If she likes to make a lot of fried food, then using the right frying technique of very high temperature frying means the exterior of the food is seared and sealed and there's not much absorption of the oil...

Try to stick with healthy oils like olive, peanut, safflower, etc.

Seed oils or olive oil are much healthier. All oils are very calorie dense but seed and olive contain more heart healthy fats.

It will have a lot of excess fat in it