Grade 4 LP must be very painful! There is no other way but surgery. Whatever damage is done, can't be reversed and it will only get worse! Grade 4 is the worst, but the pain can get worse and she may not be able to walk later in life because of how painful it is and also the worn away cartiledge (that can't be repaired).
I have 2 dogs that both have LP in both rear legs. Roxy is finally out of her surgery and healing time. She is a BRAND NEW DOG!!! It is amazing.
TJ (her 1/2 brother) will have surgery in a few months.
My advice would be to find a EXCELLENT Ortho Surgeon Specialist and go from there. (But I would definatly not wait too long for this LP surgery, she is young and in Grade 4)
Best of Luck!