Need Shrinkie Advice

Hello, I'm am fairly new to the extension world, but am getting really into it and loving it. My mother wants me to do her hair using the shrinkie method but I have some major concerns. First of all her hair is short and she does'nt reaaly want to add length but mainly volume. Her hair is 3-4 inches.
Secondly she has extreme fine hair and some thinning especially around the crown. What I had thought of was putting the shrinkies well way from the thin spots but leave the hair long enough to cover or at least minimize those areas. I haven't used shrinkies yet but I'm thinking that I can cut very small strands and pretip myself and the shrinkie will shrink enough to fit the hair and not be too bulky. Maybe I can put enough small ones to give her the volume she's wanting. I so badly want to do this for her. She's always hated her hair and I think this would make her feel so much better. Any advice and/or opinions would really be apprecited.
Thanks in advance!!