% !TEX TS-program = XeLaTeX

\documentclass{memoir}
\usepackage{xltxtra}

\usepackage{polyglossia}
\setmainlanguage{english} 
\setotherlanguage{arabic}
\usepackage{bidi}

% Define the footnote rule for the series A apparatus before loading ednotes
% This will pass along these commands to the ednotes definitions of the
% A series apparatus
\makeatletter
\newcommand\rtfootnoterule{\right@footnoterule}
\newcommand{\SelectAnoteRule}{[1]{rt}}
\makeatother
\usepackage[modulo,right,perpage,para*]{ednotes}



%%% Ednotes commands %%% 
\modulolinenumbers[1] 
\PrecedeLevelWith{A}{\setRL} 


%% The uncommented lines below are changed for typesetting the 
%% apparatus in Arabic. 
\renewcommand*{\linesfmt}[1]{\raisebox{1ex}{\linenumberfont #1}~}% 
\renewcommand{\lemmafmt}[1]{#1~[ }%
\SelectFootnoteRule{default} 
\DeclareNewFootnote[para]{B}[arabic]
\SelectFootnoteRule{extra}
\DeclareNewFootnote[para]{C}[roman]
\renewcommand\extrafootnoterule{}
\setmainfont{Charis SIL}
\begin{document}
\chapter{A chapter}
\begin{linenumbers}

This is some text. \Anote{Left}{Right} This is some more text. \Anote{Left}{Right} This is some more text.\footnoteB{A B footnote}. \footnoteB{Another B footnote.} This is some more text.\footnoteC{A C footnote}
\end{linenumbers}
\chapter{Second Chapter}
% In the chapters that don't use the RTL footnotes, I assume that you just
% want to use footnoteB (or C) but not the A apparatus.  If this incorrect,
% then my solution doesn't work.  But pressing on with this assumption,
% we need to change the footnote rule back to the left rule again.
\makeatletter
\renewcommand\rtfootnoterule{\left@footnoterule}
\makeatother
This is some text. This is some more text. This is some more text.\footnoteB{A B footnote}. This is some more text.\footnoteB{Another B footnote.} This is some more text.\footnoteC{A C footnote}
\end{document}