Arieta,
Glad to learn that you think it's the right christening; it certainly seems to fit
quite well.
A pity that your aunt seems not to have left very good signposting in her research notes
to indicate which sources she used for each part of her work -- that would obviously have
helped you a lot in undertaking your current "audit". The fact that she had a
date of birth for Jane Morris, not merely a date of baptism, suggests that she had found
something more than a PR entry -- such as notes in a family bible.
With ref. to your query
Are you able to determine if the Anne born 1813 to Wm and Anne Morris
has siblings?
as you doubtless know, the LDS FamilySearch website has an excellent search feature for
the children of pre-defined parents, which is a very convenient way of tracking down
siblings; but the LDS coverage of church registers in Wales is not at all good, so that
method yields nothing via their own data extraction program. However, for a little while
now they have had in place a cross-referencing deal with FindMyPast, who have been
undertaking a major digitisation project of their own for Welsh PRs. That does serve up a
number of other possible sibling refs. at Llanfwrog -- and this screen should show Jane
Morris's own entry there
https://familysearch.org/pal:/MM9.1.1/KCPY-7H8 (if it is not
merely a temporary search-specific URL).
Aside from FamilySearch, I am not aware of any good sibling search facility available
online. So I think the best substitute approach would be via the Clwyd Family History
Society's hardcopy transcripts of Llanfwrog PR. Unfortunately I have no copy myself,
nor the near term prospect of being able to get back to a library that has a set of them
available. Maybe somebody with access to the CFHS version will see your post and take a
look for you. Alternatively, you could arrange to have a copy mailed to you, via the
society's website --
http://www.clwydfhs.org.uk/publications.htm
Rol