Do the eyelets look ok? Another tip I've come across is to soak the line in water overnight if you're having issues with breakage.
Alternatively, you could replace the head. I'd convinced my mum to buy the Flexvolt trimmer for herself (dear old duck was talking about buying a 2-stroke, she's retired with arthritis and that's just a big old nope), today I finally received and swapped out the horrible DeWalt head/spool with a Speed-Feed 350, even casual observation showed it to be a far nicer head compared to the stock offering. Even nicer was that I didn't have to use any of the adapters provided, went straight on.