OK, one of my good friends just dropped off a racquet with me. She's a 16 year old girl, and doesn't play much, maybe once a week or every 2 weeks, sometimes more sometimes less, but just recreationally. She has a Ti S2. All I have in stock right now is Lightning XX 17 ( I usually use this for middle aged women) and Duraflex 16 (my personal string). Which should I put in her racquet. Thanks, moos.