User blog comment:B214/Volume 22 spoilers/@comment-73.46.6.122-20161126201153/@comment-9595671-20161201154936

I think it also has to do with Asia having no offensive capabilities at all, while Valerie is able to so what Gasper can since she's also a Dhampir (as Gaspar doesn't require Issei's blood to use it, but it it at full power), so she has some level of offense unlike Asia.