Moshe enacted the seven days of Mishteh (nuptial feasts, for a Besulah), and the seven days of Aveilus. He did not enact anything for a widow;

Even though you say that he did not enact anything for a widow, she needs Brachah (Birkas Chasanim). We learn from Bo'az;

It says "va'Yikach Bo'az Asarah Anashim mi'Ziknei ha'Ir va'Yomer Shevu Po va'Yeshvu";

Inference #1 (R. Alexandri): A smaller person may not sit until the greater person tells him to sit.

Inference #2 (R. Pinchas): Beis David (i.e. people from Yehudah) do not count towards the number in their [nuptial] feasts. (If not, it would have sufficed to take nine others. - MEICHAL HA'MAYIM)

Inference #3 (R. Lazar bei R. Yosi): Birkas Chasanim needs 10 people.

(R. Yudah bar Pazi): This is not only for a bachelor who married a Besulah. Rather, it is even for a widower who married a widow, for Bo'az was a widower, and Rus was a widow!

Question: It says "Va'Tehom Kol ha'Ir Aleihem" - is it possible that the entire city was astounded due to Na'ami's downfall?!

Answer: Rather, Bo'az' wife died that day. The entire nation bestowed Chesed (came to her funeral, so they saw when) Rus entered with Na'ami. It turns out that this one left (died), and this one (Rus) entered [Bo'az' house].

(Beraisa): We say Birkas Chasanim all seven days.

(R. Yirmeyah): We take the Kalah out to the Chupah all seven days (for Birkas Chasanim).

Question (R. Yosi): R. Chiyah taught that we say that Birkas Avelim all seven days. Can you say that we take out the Mes all seven days?!

Question: What was the conclusion?

Answer: Just like here, we remember [the mourning, and we bless, even without the Mes] - also here, we remember [the Simchah, and we bless, even without the Kalah].