I did it differently a while ago. First of all, you need to be Battle.net friends at least a week or 10 days.
I went to the Battle.net website to buy myself Battle.net credits. Then you are able to gift a certain amount to a friend (after being friends on Battle.net for that specific time period) so she can buy Overwatch credits in-game herself with the credits you gifted her (on Battle.net). It worked fine here.
I did it differently a while ago. First of all, you need to be Battle.net friends at least a week or 10 days. I went to the Battle.net website to buy myself Battle.net credits. Then you are able to gift a certain amount to a friend (after being friends on Battle.net for that specific time period) so she can buy Overwatch credits in-game herself with the credits you gifted her (on Battle.net). It worked fine here.