Hi,
Some people just can't have acylic on their nails, it's hard to tell if your L&P is thick enough without seeing them, how do they start to come off, do they lift, crack and break, tip...ect. When they come off are they clean underneath ( if they are complete) or cloudy...
Another alternative is to try a different system on your sister. maybe gel or fibre would be more suitable. How old are they and what is their life style like? All these are questions you have to ask your self when you are trying to solve a problem.
I hope this helps honey...my moto is always, that if you don't suceed to try, try and try again.