One thing to consider with an eternity band is if you want the diamonds to go all the way around or not. If they go all the way around, she should be careful with it, which may limit how she can wear it. Also, it may be more difficult to resize, although a jeweler with a laser welder can resize eternity bands with diamonds that go all the way around. It can be a challenge, however, to find a local jeweler who has a laser welder. You should ask if the vendor you buy it from if can resize it in the future, if it is a concern for you.
On the other hand, it's nice to have the diamonds go all the way around because then you don't have to readjust it to have the diamonds on the correct "side".
I have an eternity band with a very small 4 mm solid gold part, to allow for resizing. The solid part is so small that I don't have an issue with it spinning all the way a round, in general.