I would not buy hoppers based on what you said in your post. The 4 day hoppers are not much less expensive on a per day basis than the 1 park/1 day tickets.
1 Day/1Park tickets are $53 (adult)
4 Day hoppers are $210.94 (adult at the gate) or $203.52 adult advance purchase)
FWIW, all of the prices above include taxes.
If you buy the 4 Day hopper tickets in advance, that works out to $50.88 per day. To me, the "$6.36 savings" on a future trip is so not worth spending an extra or $150.52 per adult now! That would be especially so if I didn't need to "park hop" on this trip.
If you go to both MGM and the MK, and have to each buy two 1 Day/1 Park tickets, it definitely wouldn't be worth it!
You can get two adult 1 Day/1 Park tickets (used to be called Bounce Back) for $100.70 or $50.35 per park day if you buy them at the same time. That's less than the per day cost of the 4 Day PH ticket! Do keep in mind that you can't hop with the one day tickets and if you choose this option, the same person has to use both tickets. Disney puts names on these tickets. (In other words, you can't buy these and have two people go to the same park on the same day).
Here's a link to ticket prices if you want to do the math for yourself or for your daughter's ticket"
http://www.wdwig.com/ticketchart.htm
Enjoy the trip!