I don't think it matter what language she learns. Any language is an asset.
I would argue that employment is probably not an issue that you need to worry about. There are plenty of jobs for people who are fluent in European languages and if she learns one language then learning a 3rd language will be easier if she does decide that she needs it later. Also because European languages share a common root being fluent in one will make it much easier for her to understand another.
If you are fluent in French then maybe that is the best language because you can practice together between lessons. I think that in any language where learning is based on 1 or 2 hours formal instruction a week what happens between the lessons is very important. If you don't practice your vocab etc then you won't progress fast.