Being Real – Fortunately for you I happened to recently pick up a book in shul that was exactly on this topic. The book is Titled Shemos HaAretz and is authored by Rabbi Shmuel Baruch Genut. It is a compilation of sha’alot that he asked to HaRav Chaim Kanievsky, shlita on the subject of names. It was quiet interesting.
You can use a translator to view this site about the book:
http://ladaat.info/article.aspx?artid=4299
Being that I only read through the book once I haven’t absorbed every detail. However, this much I do remember.
It is advised not to marry a girl with the same exact name as your mother. If either your mother or the girl have more than one name and they share one of them, then it depends on what name people know them as. For example:
If your Mother’s name is Sarah Leah and the girl’s name is only Leah, I believe he says it would be a possible problem if your mother goes by both names, Sarah Leah. However, if your mother is only known by others as Sarah, then it does not matter (according to all sources) that they share the name Leah. Note, however, in your parents house your future Kalah should be called by a nickname like Lealeh.
I do not remember if according to HaRav Kanievsky it matters whether we are talking about the Kallah/Shviger or the Chosson/Sh’ver.
In your personal case I must agreed that if you are interested in either of them you should first consult with your posek as there may be a machlokes concerning following this minhag.
BTW – from what I read it seems that the main issue is a concern for Ayin Harah.
NOTE TO ALL COMMENTATORS: It is nice to try to help another yid, but when doing so don’t base it on “hearsay”. You are not truly helping them and you can possibly be causing yourself serious unnecessary Onish min Hashamiyim.