Thinner hair treatment and trim schedule?

[TheVegan6]

Hello! My hair is not thin, but my mother, with beautiful, shiny hair, is wondering how to prevent her ends from getting too thin. Does anyone know a nice trim schedule for her hair to remain full at the ends but keep growing? She is currently almost BSL, and she is growing out layers. Her exact hair type is 1b/C/i/ii.
She treats her hair very well. She washes with a sulphate free shampoo, uses cone-free conditioner, wears it up most of the time, never uses heat or dye, and brushes her hair with fingers or a comb.

[Crumpet]

You could check out the microtrimming and maintaining thread. I'm planning on joining them in a few weeks to help me thicken up my hemline and still grow.

[UP Lisa]

Since her hair is course, unless she is really rough with it, she probably won't need to trim it all that much. Maybe half an inch every three months.

[Coolcombination]

I would say, with a growth rate of 0.5" a month that to maintain a good hemline and thick ends personally cut 0.5" every 2-4 months.