There is no simple answer to this question as different mums have different preferences. Some mums prefer sun, while others prefer shade. The best way to determine what your mum likes is to ask her directly or observe her behaviour.
If your mum enjoys spending time in the sun, she may be more likely to plant her garden in a sunny spot. However, if she prefers spending time in the shade, she may choose to plant her garden in an area that gets less sunlight. Ultimately, it comes down to what makes your mum happy and comfortable.