Plantronics legend if she just wants overall best function. (Design could be an issue if she wears glasses.)
Jawbone era if she wants it to be sleek/slim. This also has the best noise cancelling feature out of them all. (Not the best at staying in your ea, so it will need adjustment from time to time.)
I've tried a lot of the higher end ones and here are some to avoid.
1. Bose: I forgot the exact name but I had the version 2 and while it is tiny and sounded great, it did not do well with ad2p and did not have the best noise cancelling. When it was windy, people had issue hearing me and if you are listening to music or podcast on it, it would turn off on you after so many minutes.
2. Motorola Elite Sliver: This thing is comfortable and sounded good and can have multiple devices attached. Everything was great until I used it outside with no real background noise. No one could hear me unless I was shouting and even then they had trouble understanding me. When used inside with no noise whatsoever, it worked fine. Also the start up is annoyingly long. When I turn it on when already on a call, it would say "power on, phone 1 connected, phone 2 connected" with delays in between each one and it would be a good 5 seconds before it started to transmit what the other person was saying.
I've used a lot more but these are my most recent experiences.