I suggest a short checklist before you contact anyone:
First, take a look into your spam folder. It may occur that a manager
forwards your email to his/her private mailbox and later replies from
that non-company internal address, which would cause the company's
spam filter to be applied.
Then check the "missed calls" lists of every telephone/mobile phone
that you are using. Also check inboxes of apps like WhatsApp,
When you feel certain you didn't miss a message, create an email
draft to the manager, but don't send it. If you are using MS Outlook, which I suppose here, you might be shown an absence
notification. This step may reveal that she is currently not
available (holiday, illness) and was not able to answer yet. Be sure to delete the email draft afterwards, in order not to accidentally send her an empty mail later.
Take a look into her calender (again, I'm supposing an Outlook infrastructure). Usually available timeslots are marked different from blocked ones. She might have marked some weeks as "absent", without creating an absence notification.
Now you are certain that your application was not answered yet though there had already been the chance for her to do so.
An elegant way to contact her would be a different (real) question or some important information concerning your or her work which could start a conversation. Let's say, you would like to move from backend development to automated testing centre. Then your question could be something about a failed test in the recent past; or a suggestion about new tests that would be possible, but have not yet been developed. Be creative, and be sure that the question is so good that she won't even think about the possibility that it was designed as a conversation starter. She must have a real benefit from your call.
But what would I do if I had no reason to call her except to ask about the application?
When applying to a new employer, I used to wait up to six weeks until I asked them about status. But since it's an internal application in your case, I would consider three weeks perfect, because your data is most likely already saved in your Human Resources Database which she can access. That should make things faster.
Mondays, though, in my opinion are bad because on Mondays everyone is preparing their work for the new week, or some cleanup from last week still needs to be done. (Fridays are probably bad too due to early leave.)
So I suggest: Ask her on next Tuesday.