Is there a replacement for cheese on pizza?
Depending on how much she doesn't like cheese, and what she doesn't like about it, you have a few options. You may even be able to preserve the appearance of pizza. 


Ricotta is sometimes used (even without tomato sauce and with a green vegetable); while technically cheese it doesn't have the texture or the taste you'd normally think of as cheese, but will help things adhere. 
Some of the vegan cheese substitutes now melt like cheese, and some taste like cheese, but few do both - a careful reading of reviews may find one that fails to match cheese in the way she doesn't like. 


But assuming they don't go far enough, you'll have to get more creative. Folding over the edges of the dough will help stop things falling off. A much thicker sauce is also useful; with some (e.g. corn) starch in it, it will thicken further around the topping as it cooks. Mixing the toppings into the sauce will help stop them overcooking. Flatter toppings like sliced tomato/sausage, or bacon cut from rashers rather than cubes, will also stick better than round things. Or go cross-cultural, and use refried beans under salsa for a "Mexican pizza" that's neither Mexican nor pizza. 

A fairly thinly topped base with more on the side than you'd normally expect would be a practical way to serve it, if you're still worried about things staying put. 

There are plenty of ideas for pizza without cheese. Most are vegan, but you can adapt them assuming you're not.