We saw Mulan at the Norway Character Breakfast in May last year.
I have also seen Mulan in China a lot. I also saw her once near the international gateway between France and England. She just appeared with two other princesses.
I know your daughter's pain. I have a Mushu obsession. I once went to three parks in one day looking for Mushu. When I finally found him I told him I had been looking for him. He took a long time writing in my autograph book and when I read it it said he was sorry he had missed me but he was out saving China! So cute!
Anyway, as far as the character hotline is concerned you can check with any CM near a phone and they can call a character hotline and find out where Mulan might be that day. This will work at any park, ie you can ask someone in MK and they can find out where she will be even if she will be in Epcot.
My suggestion is first thing every morning check with the Guest Relations office in whichever park you go to and see if she will be out that day. They have a tendancy to say, well not right now but check back in a few hours. So you may end up checking in a lot.
My last suggestion is to call the restaurant directly, there is a thread on here somewhere that has all of the restaurant numbers - I think it's in the cake thread. Tell them how much your daughter loves Mulan. Tell them the day you have your breakfast ressie. Tell them about what happened in December and how your DD has been talking about it ever since. You never know what could happen, this is the year of a Million Dreams.
As an anecdote, last year we wanted to see Jiminy Cricket. We'd heard that he'd been out and about in AK. My mother loves Jiminy and when we checked in at Guest Relations that morning in MK to check on the character hotline we were told to wait. The CM was gone for a while but then she came back and we were whisked away behind stage in a Disney van over to AK to see Jiminy. We didn't have a park hopper for that day and we got to the park at noon so we didn't want to pay for another ticket. So you never know, dreams can come true.
And if you do call and tell them all of this ahead of time, I would try to stop in at Guest Relations, preferably, a day before your ressie and remind them of your request. The princesses work on a rotation at Norway, I think the only guarentee is Belle so if they have a reason to rotate Mulan in, I bet they would do it.