Is a husband's request to his wife, who is married and a mother, to spend from her university allowance on her study needs, while he covers whatever else she needs and expenses related to food, drink, and clothing, considered an encroachment on her wealth?

Your participation with your wife in her study expenses is an act of kindness on your part and is not obligatory for you. There is no harm in taking some of her money with her willing consent, even if it is to spend on your personal needs, as Allah Almighty says: "But if they give up willingly to you anything of it, then consume it with pleasure and ease."