Hi Malky, thank you very much for your reply!
Yes, I believe I have seen the latest version of Burke's, after consultation with the editor of
www.thepeerage.com, who also cites Mabel as daughter of Gerald and Julia with reference to Burke's. However it doesn't seem to shed more light on the matter, as I suspect one of the earlier sources must be erroneous somewhere, and that subsequent genealogies on the Aylmers have based it on this error.
Not claiming to know much about renaissance tombs of the Irish nobility, yet the inscription mentioning two children of the marriage seems to me to be of dire importance with regards to Mabel's identity. If she was indeed a legitimate daughter of the Aylmers, why was she not mentioned on the tomb inscription? Was she born after the creation of the tomb? Was she illegitimate? Or adopted, perhaps?
Best regards