Is it permissible for a woman whose husband has passed away to go for 'Umrah after (four months and ten days) if some of the months have 31 days, or must she complete the full month?

What is considered religiously valid in calculating the 'iddah (waiting period) and other legal rulings are lunar months, not solar months, due to the Almighty's saying: "Indeed, the number of months with Allah is twelve months in the Register of Allah, the day He created the heavens and the earth; of these, four are sacred." A lunar month is either twenty-nine or thirty days.