Do you mean Illness Benefit which is based on PRSI contributions, or Disability Allowance which is means tested?
If you mean Illness Benefit, you may be entitled to half-rate payment in addition to your One Parent Family Payment if you satisfy the qualifying PRSI conditions.
If you mean Disability Allowance, which is means tested, you could not receive it in addition to One Parent Family Payment. You would only receive one or the other.
Check out www.welfare.ie for information on how you qualify for Illness Benefit.