I don't think there's enough context to definitively answer your question. Both are grammatically correct, but one form may be better than the other in a specific context.
If your asking her was the final event in a series of events, then the simple past seems more appropriate than the present perfect.
If you plan to ask her again, or if you plan to have someone else ask her for you, then the present perfect seems more appropriate because present perfect implies a continuing saga.
Provide sufficient context and you might get a more satisfying answer to your question. It's potentially an interesting question. I'm interested in what everyone else thinks about when to use the simple past versus the present perfect. I have my own ideas, but even though I don't know what everyone else thinks, I know that what I think isn't necessarily what everyone else thinks.