My young sister who doesn't play on a high level broke her strings. She never restrings and has a low 3.0 game, the string I was thinking of is poly main, syn gut cross. Her last string she played more than a year with before restringing and that was a fully poly. What tension would you recommend for a player like this?
There's a better than average chance (much better?...) that poly is working against her. That's a control string that primarily helps really big hitters at the college level - even college bound - and above. It takes a lot of swing speed to physically bend that string and make it perform as intended.
Yes it's rather tough, but it "goes dead" long before it physically breaks. And it's generally less resilient than softer string types. That means less "free power" and it can also more readily transmit impact shock into a player's wrist and elbow. The popularization of poly strings among recreational players over the last decade or so has brought about an explosion of wrist, elbow, and shoulder issues/injuries for players at just about every level.
If she's playing at a low 3.0 level, a 16 ga. synthetic gut tensioned at a pound or two above the middle of the recommended range on her particular racquet might be a good option. Even if it doesn't last a whole year, she can buy a full reel of the stuff for $35-$45 and pay a stringer for the installation. Multifiber is a comfortable option, but I'm not wild about it unless somebody needs a softer alternative. Multi is comfortable, but it tends to steadily degrade and soften as it's played. I prefer the service life and performance (and reasonable comfort) of syn. gut.
