The launch comes nearly two weeks after rockets fired from Lebanese territory hit the Jewish state in the first such attack in two years, and comes two days after a roadside bomb struck French peacekeepers in southern Lebanon.
The attack follows rising concerns that conflict in next-door Syria may spill into its neighbor, where the public is deeply divided between supporters and opponents of the Syrian regime.
Lebanese see regional powers including Syria as having sponsored violence in their country in the past, to send messages to each other or to settle accounts.
This latest rocket was fired late Sunday from the southern village of Majdal Silim and hit a home in Houla, another village close to the border, the army said in a statement. The statement said the woman was seriously wounded and her home damaged.
The army said troops cordoned off the area where the rocket landed and intensified patrols in the place where the rocket was launched. It added that a military committee began an investigation.
U.N. peacekeepers based in southern Lebanon confirmed the rocket launch and the injury, and said they would work with the Lebanese army to try to contain the "escalation of incidents."
Early Monday, warplanes were seen flying at high altitude over southern and eastern Lebanon as well as the capital Beirut.
Israeli warplanes and drones frequently fly over Lebanon but it was not clear if these flights were related to the rocket attack.
The southern border has been tense, but largely quiet, since Lebanon's Hezbollah group and Israel fought a deadly 34-day war in 2006. During the fighting, Israel bombed Hezbollah's strongholds in Lebanon, and the militant group barraged northern Israel with nearly 4,000 rockets.
About 1,200 Lebanese and 160 Israelis were killed in the conflict, which ended with a U.N.-brokered truce that sent thousands of Lebanese troops and international peacekeepers into southern Lebanon to prevent another outbreak.
There have been several rocket launches since the 2006 war, but Hezbollah has not claimed responsibility for any of them. Smaller Palestinian factions, some linked to al-Qaida, have claimed to have launched rockets on several occasions.
The latest rocket launch that reached Israel, the first in two years, happened in November. There were no casualties.
Sunday's launch came two days after a roadside bomb hit a U.N. vehicle in southern Lebanon, wounding five French peacekeepers and a Lebanese bystander.
France's foreign minister said Sunday that France had "strong reason" to believe that Syria was behind the blast. Alain Juppe told RFI radio that Paris believes Hezbollah was also involved, but has no proof.
Syria's foreign ministry on Monday denied that the country had any role in the attack against the peacekeeping force, known as UNIFIL. The ministry said in a statement that Juppe's comments "fabricate and forge facts about Syria."
The two incidents come amid fears that violence in neighboring Syria might spread into Lebanon.
Damascus dominated the tiny Mediterranean nation for three decades until it withdrew its troops in 2005, and retains close ties with numerous Lebanese factions including Hezbollah.
Syrian President Bashar Assad is facing international condemnation for brutally crushing an uprising against his rule, and France has been among his fiercest critics.
Some Lebanese politicians, including former Prime Minister Saad Hariri, have said the attack on the peacekeepers was a Syrian message responding to Paris' criticism of Assad's crackdown.
Many also fear that the heightened emotions caused by the Syrian conflict could lead to an outbreak of violence in areas like the northern city of Tripoli, where Sunnis and Alawites in adjoining neighborhoods have clashed in the past.
Assad's regime is dominated by the Alawite sect, an offshoot of Shiite Islam, while the Syrian opposition is heavily Sunni.
The Spanish head of UNIFIL expressed "serious concern" at the rocket launch and the two other "security breaches" in the south over the last two weeks.
Maj. Gen. Alberto Asarta Cuevas said the force would take concrete measures, together with the Lebanese army, to reinforce security in the area.