Name Change in AD

There should be no implications with doing this.
In Active Directory Users and Computers right click on the user and select rename, make sure that you change all the settings.  Do not select properties and change it this way as you will miss some of the settings.

add her new name as the email address and alias the old address to catch any legacy emails.

Active Directory change shouldn't be a probem.

don't forget to uncheck the the box below the email addresses to not use the recipient policy as this might remove the old address

For the most part you don't have to worry but there are some things you have to think about.  Take a look at this question Americom and I answered last year, concerns covered here:

https://www.experts-exchange.com/questions/24607520/changing-a-uername-in-AD.html

Thanks

Mike

There aren't any real problems doing this...but I find it "better housekeeping" to just create the user a new account and move their profile over.  Things like the Exchange profile don't get renamed, and that can be confusing if you ever move exchange servers or have to do an exmerge.

On last comment: If all she wants is that her email be XY.Z instead of XY.A do I have to change her login and details in AD.