It appears the solicitor is acting for both the ex & her mother, as otherwise there seems to be no reason for letters to be sent detailing what the mother wants. If that is the case, then I don't see that there is a conflict of interest - unless the interest of the mother conflicts with that of the ex, which seems unlikely - but it certainly raises a question mark over use of the ex's legal aid to do work for the mother. However, how do you know this is what is happening? Might it be that the mother has instructed the solicitor separately & is paying her, or has her own legal aid?