Coumadin dosage and INR

Is there a definite guideline between the coumadin dosage required and
INR reading, or it varies from patient to patient? My mother has been on coumadin 2.0 mg for approx 18 months and during this period of time her family doctor took INR tests once every two months but never adjusted the dosage. During this 18 months my mothers has been treated with stomach bleeding (immediate cause being an ulcer developed when she took Actonel without sufficent water) and CHF on 2 other occasions.
Well at her last time at the hospital for CHF (end Nov) her sodium level was 118 and INR well over 4. During her hospitalization, the doctor adjusted her coumadin from 0.5 mg to 2 mg depending on her daily INR test which were between 2.39 to 3.38) She took 1mg on her day of discharege and has been on this dosage for a few days.

Today she visited the *family doctor*, who took INR reading (1.9) but seemed to think if 1mg was what the hosp said, then 1mg my mother will take. It'S amazing that this doctor never had any opinion of her own.
As per hospital record when the INR was 2.39 they gave her 2mg.

I was just thinking if all these traumar my mother suffered has to do with incorrect coumadin she has been taking for year and half. Dr
Chung, any comments? thanks in advance