My wife is allergic to sesame, What can be used to substitute for the tahina?

You can also leave it out, just use chickpeas, add olive oil and additional ingredients, drizzle a little extra olive oil on top.

A friend of mine uses almond butter and or macadamia nut butter for the same reason. Her hummus is always a huge hit.

Try various seeds and nuts that you both like and can tolerate.
Then make an adapted version of tehina sauce using one of them instead of the sesame.
For example, here's one using peanut butter (from Nigella Lawson about 5 years ago) which tastes very good.
https://www.nigella.com/recipes/peanut-butter-hummus
Also have a look at this chart of the fat in various nuts and seeds....
http://nutritiondata.self.com/foods-012015000000000000000-w.html?maxCount=88
If you use some close to sesame seed in fat, probably use same volume as the recipe calls for.
But if you use, say, pecans or macadamias, which have about 50% more fat than sesame, you might want to reduce your amounts of those nuts compared to Ottolenghit/Tamimi recipe.