Susanna Dickinson lived in Gonzales in Mexican Texas with her first husband, Almaron Dickinson. As the Mexican government increasingly abandoned its federalist structure in favor of a more centralized government, Almaron Dickinson became one of the early proponents of war. The men quickly herded cattle into the Alamo and scrounged for food in some of the recently abandoned houses. A few members of the garrison brought their families into the Alamo for safety. Susanna Dickinson and her daughter Angelina were among these. For the next twelve days, the Alamo lay under siege. Santa Anna planned an early morning assault for March 6. At 10 pm on March 5, the Mexican artillery ceased their bombardment. As Santa Anna had planned, the exhausted Texians soon fell into the first uninterrupted sleep many had gotten since the siege began. At 5:30 a.m. Santa Anna gave the order to advance. As the Mexican soldiers began to yell and their buglers began to play, the Texan defenders awakened and rushed to their posts. Dickinson and her daughter gathered in the church sacristy with most of other noncombatants for safety. She later mentioned that Davy Crockett stopped briefly in the chapel to pray before taking his assigned position.

The Mexican soldiers soon breached the outer walls of the Alamo. As previously planned, most of the Texans fell back to the barracks and the chapel. In the confusion, Almaron Dickinson slipped from his post manning a cannon in the chapel to join his wife in the sacristy. He yelled "Great God, Sue, the Mexicans are inside our walls! If they spare you, save my child!", then kissed her briefly and returned to his cannon. It took an hour for the Mexican army to secure complete control of the Alamo. The last of the Texans to die were the eleven men, including Almaron Dickinson, manning the two 12-pound cannon in the chapel. The entrance to the church had been barricaded with sandbags, which the Texans were able to fire over. A shot from the 18-pound cannon destroyed the barricades, and Mexican soldiers entered the building after firing an initial musket volley. Dickinson's crew fired their cannon from the apse into the Mexican soldiers at the door. With no time to reload, the Texans, including Dickinson, Gregorio Esparza, and Bonham, grabbed rifles and fired before being bayoneted to death. Texian Robert Evans, the master of ordnance, had been tasked with keeping the gunpowder from falling into Mexican hands. Wounded, he crawled towards the powder magazine but was killed by a musket ball with his torch only inches from the powder. If he had succeeded, the blast would have destroyed the church, killing Dickinson and the other women and children hiding in the sacristy.

As soldiers approached the sacristy, one of the sons of defender Anthony Wolf stood to pull a blanket over his shoulders. In the dark, Mexican soldiers mistook him for an adult and killed him. Possibly the last Texan to die in battle was Jacob Walker, who attempted to hide behind Dickinson and the other women; four Mexican soldiers killed him in front of them. Another Texan, Brigido Guerrero, also sought refuge in the sacristy. Guerrero, who had deserted from the Mexican Army in December 1835, was spared after convincing the soldiers he was a prisoner of the Texans. In the confusion, Dickinson was lightly wounded.

On March 7, Santa Anna interviewed each of the survivors individually. He was impressed with Dickinson and offered to adopt Angelina and have the child educated in Mexico City. Dickinson refused the offer, which was not extended to fellow Alamo survivor Juana Navarro Alsbury for her son who was of similar age.

Santa Anna ordered that the Tejano civilian survivors be allowed to return to their homes in San Antonio. Dickinson and Joe, a Texan slave, were allowed to travel towards the Anglo settlements, escorted by Ben, a former slave from the United States who served as Mexican Colonel Juan Almonte's cook. Each woman was given $2 and a blanket and was allowed to go free and spread the news of the destruction that awaited those who opposed the Mexican government. Before releasing Joe, Santa Anna ordered that the surviving members of the Mexican army parade in a grand review, in the hopes that Joe and Dickinson would deliver a warning to the remainder of the Texan forces that his army was unbeatable.

When the small party of survivors arrived in Gonzales on March 13 they found Sam Houston, the commander of all Texan forces, waiting there with about 400 men. After Dickinson and Joe related the details of the battle and the strength of Santa Anna's army, Houston advised all civilians to evacuate and then ordered the army to retreat. This was the beginning of the Runaway Scrape, in which much of the population of Texas, including the acting government, rushed to the east to escape the advancing Mexican army.

Susanna Dickinson reported, after the battle, the following had occurred during the siege and ultimate fight;

Some points of Dickinson's account were confirmed by other survivors, including Enrique Esparza, the son of Alamo defender Gregorio Esparza. Joe confirmed other statements.

Illiterate, Susanna Dickinson left no written accounts of what happened in the Alamo, but did give several oral accounts, with them always corroborating what she had previously stated. She remarried soon afterward to a man last named Williams, in 1837, but divorced almost immediately afterward on the grounds of cruelty. She married a third time in 1838, last name Herring, with that husband dying due to alcoholism. Dickinson married her fourth husband in 1847, last name Bellows, but the couple divorced in 1857 allegedly due to her having an affair. In 1858 she married for the fifth and final time, to J. W. Hannig, a cabinet maker, and with whom she would remain for the rest of her life. Dickinson died in 1883 and was buried in the Oakwood Cemetery, with the following inscription:

"Sacred to the Memory of Susan A. Wife of J. W. Hannig Died Oct. 7, 1883 Aged 68 Years."