Mini mal is the go...
But what are you riding?
If it's a short board... then eventually, she's going to want the same.
If you're budgetting.... Go for one of those ugly foam type surf boards you see all the beginner schools use. They are heaps cheaper than buying a mini mal that she might want to dump later on.
Once she gets the hang of it.... she can decide whether she's a 'longish boarder' or a real surfer.

It's like buying a guitar. Don't spend heaps on something that eventually will never be used.