The 64-year-old Calgary-Fish Creek MLA said the decision was made for "personal reasons."
"At this time I'm doing one day at a time, so I will see how things go over the next few weeks," Forsyth said at the Wildrose annual general meeting.
Forsyth has been dealing with hearing issues and now travels with a service dog that can alert her to different sounds.
The dog even accompanies her into the chamber of the legislature.
Forsyth, a six-term MLA, has been in politics for more than 20 years.
She was elected as a Progressive Conservative under former premier Ralph Klein in 1993 and by 2001 was in cabinet, as solicitor general and as children's services minister.
She launched Alberta's Amber Alert program and steered through legislation to protect drug-endangered children, two programs she cited Friday as career highlights.
"I've been very fortunate to be able to help people and very fortunate to bring forward ground breaking legislation in this country," she said.
In January 2010, she and fellow Tory Rob Anderson crossed the floor to join the fledgling Wildrose.
At the time, Forsyth had been critical of then-premier Ed Stelmach's leadership. Stelmach dumped her from cabinet after the 2008 election.
Forsyth said Friday that going to the opposition meant learning to research and speak on the fly on a variety of issues compared with focusing on one area as a cabinet minister.
She remembers once having to speak to a bill on a moment's notice with no chance to prepare.
"As a member of the opposition, you have to literally learn every bill that's coming forward in the legislature," she said.
She said it's been a wild ride, going from government backbencher to cabinet minister and finally to opposition critic.
"The biggest thing is I've been blessed with going full circle," she said. "How many MLAs in this country can truly say they've had that?"
Forsyth is only one of two Wildrose MLAs in Calgary. The other is Jeff Wilson in Calgary-Shaw.
Her resignation will put in play a key riding Forsyth narrowly won in the 2012 campaign. She defeated Tory Wendelin Fraser by just 38 votes.
An early departure could trigger a byelection at a time her party is still rebounding from four byelection losses to the Tories on Oct. 27.
Forsyth said she is aware of that, but said it remains "a family decision. I have to make that based on what's right, so that's what I'm going to do."