Susan Collins has always been her own Senator, but with the looming departure of fellow Maine Republican Sen. Olympia Snowe, she might finally have the freedom and the spotlight to show it.

Described as a tireless worker, a “legit, real legislator” and an independent thinker by sources close to state and party politics, Collins has carved out a niche for herself within a rigid Republican Conference, particularly on national security issues. But for years, she has been paired, at least in perception, with Maine’s senior Senator: another female moderate lawmaker with whom Collins did not always agree.

“For her, in recent years, it’s been much more of a curse than a blessing, in large part because Snowe always has a tendency to carve out more liberal ground and provides little centrist cover at all,” one Republican aide said. “I think it was difficult in some ways for Collins on certain issues to express herself exactly on how she saw things because they were seen as such tandem.”

Collins said in a statement Tuesday that she was “absolutely devastated” by the news of Snowe’s retirement. And of course, if a Democrat wins the Pine Tree State’s open seat, it could create some political complications for Collins, who is up for re-election in 2014. Even the most popular of Republicans have faced primary challenges from the right in the past two cycles, even though Snowe was on track to avoid a divisive primary this year.

But Democrats now have a solid chance at winning in Maine, and voting next to a Senator of a different party — either with or against — could generate ample material for conservatives or liberals to challenge Collins.

Over the years, Snowe and Collins took several tough votes together, from helping provide the filibuster-proof 60 votes needed for President Barack Obama’s 2009 stimulus bill and his Wall Street reform bill to multiple votes with Democrats to extend unemployment insurance without offsets. But sources indicated the two Members rarely conferred before votes and in recent months have split more often. Many local news outlets covered Collins’ vote for the Democrats’ proposed millionaires surtax to pay for the payroll tax holiday. She was the only GOP Senator to break with her party.

Just last week, Snowe voted against an amendment proposed by Sen. Roy Blunt (R-Mo.) that would have granted broad exemptions from health care coverage if employers conscientiously objected to providing it. Collins voted for it.

“Sen. Collins is respected in Maine as an independent thinker who listens to people on both sides of the aisle and in the end always does what she thinks is right for Maine and the country, and that won’t change,” Collins spokesman Kevin Kelley said.

Collins is generally more popular within her Conference than Snowe and has worked to get in the good graces of Republican leadership while also reaching out across the aisle.

As ranking member of the Homeland Security and Governmental Affairs Committee, Collins has established a strong working relationship with Chairman Joe Lieberman (I-Conn.), who caucuses with Democrats. And she often speaks out at weekly Republican policy lunches.

Multiple Republican sources said that it is possible Snowe’s departure could be “liberating” for Collins, but there are still some drawbacks — especially on tough votes — to not having a like-minded colleague with whom she can return home and defend her choices.

“I think it makes it more complicated for her because she and Olympia could basically vote the same way and then go home and explain it,” another GOP source said. “Now she has two things pinning her in: a primary, which would push her to the right, and a potential Democratic colleague, which would push her to the left.”

A former Snowe staffer, however, dismissed the idea that the two Senators were ever reliant on each other for decisions. The former staffer noted that Collins is a shrewd, savvy politician who is in tune with Maine voters and has easily won elections many thought would be tight, such as her 2008 victory over former Rep. Tom Allen (D).

“She’s a very able legislator, a very smart Senator who represents the state of Maine very well,” the staffer said. “She bases her decisions on her instincts, what she thinks is best. This will have no impact on her or the decisions she makes and will, in some ways, will help showcase … her tremendous abilities as a legislator even more.”

As for those who think Snowe’s departure could put the junior Senator in a tough spot, “anyone who says that doesn’t know Sen. Collins,” the staffer added.

About one-third of Maine voters are registered independents, with the rest essentially divided equally between Democrats and Republicans. Republicans currently control the governor’s mansion and the Legislature.