When I string a Yonex DR98 or Yonex Rdis 100 (actually a 98 inch frame) at 55 lbs on a constant pull machine Alpha Ghost, the ERT 300 reads 37 Dynamic Tenuson immediately off the stringer. The player is among the best 4.0 men in town and out of the nearly 300 4.0 men in town is a among the select few chosen by 5.5 men to play 9.5 combo. There are less than 10 4.0 guys in town playing 9.5 combo out of nearly 300 men. He plays effectively with full poly for a month then restrings.
IMO,You have been wasting your money restringing your daughter's frame so quickly.
First piece of advice :
1) change the crosses to something that holds tension better (Lux 4 G is the best poly for that but I hate the string and use Head Hawk personally)
2) string the gut and crosses at a higher tension.
I personally string a lot of Guy/Poly hybrids and string them from 52M to 58M depending on the player. 57M/55X is what I use for myself and a 4.5 lady using the same Wilson Natural Gut 16g / Head Hawk 17g and the strings for 2 months. I am a 4.0 guy who has a tennisrecord projected dntrp of over 3.95. Schmke has me over the threshold to be bumped to 4.5. Whether bumped or not, that gives you an idea of my level of play.
Here is something you might watch and read:
http://www.tennis-warehouse.com/reviewvideo.html?pcode=PTG16&vid=JJI9-e8U5_E
http://www.tennis-warehouse.com/Reviews/PTG16/PTG16Review.html
Andy Gertz is an open level player who recently left TW and when he play-tested Pacific Tough Gut / Kevlar he broke the Kevlar first. Read that again.
IMO, there is no reason to restring "about 5 hours " for any rec player or junior player using gut hybrids. Poly / gut or gut / poly.
Gut holds tension longer than any string. Pick a better cross, string higher tension and your daughter's strings will last much longer.