Are you looking for other cake flavors for the other tiers?
Or are you looking for icing flavors?
Or are you looking for Filling flavors?
As for tiers, whatever she wants to serve is what she should get, the cake flavors dont' have to match, you won't be putting the two flavors on a plate for the guest to eat together.
Icing, My favorite is mary kay icing, but others swear by cream cheese
Filling, For red velvet you could do a chocolate of some sort, but I prefer whatever it is iced in.
The tradition way to serve red velvet cake it with a cream cheese filling. I work at a bakery and we fill with cream cheese add chocolate sprinkles to the side walls and a rosette of chocolate buttercream on top on the cake.
the crusting cream cheese icing on this site is very good. Just wanted to add a funny: my nephew wanted to have red velvet for his wedding cake -so I made one with the cream cheese. He and his lovely bride to be, came over and I cut the cake. Welllllll, when you cut the cake, it makes crumbs that pull through the icing. That was not going to be alright with him - he did not like the "messy cut" it made! 
I told him I did not think the person cutting his cake would wipe the knife after every cut 
!!!! Well, needless to say, he is not having red velvet. I told him most people talk about "bridezilla" - if I was not the aunt, he would be the groom from H*** in most people's books
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