Gerri Elliott, one of Microsoft’s star execs, left the company early this year to spend more time with her family. Yes, seriously to spend time with her family. As I wrote in January, her departure was a major loss for Microsoft, according to senior executives there, and it was also a case of a powerful woman asking, “Why kill myself and miss my kids growing up?”

Now Elliott, who spent 22 years at IBM before moving to Microsoft and heading the $8 billion Worldwide Public Sector unit there, has finished her hands-on familial gig and hasn’t taken long to find a new one back in the business world. Today, Juniper Networks announced that Elliott is coming on board in a new position crafted for her: EVP of Strategic Alliances.

Elliotts’s friends and former colleagues aren’t surprised. She and Juniper’s CEO, Kevin Johnson, have known each other for two decades, going back to their stints together at IBM and Microsoft. In fact, Elliott says she remembers the day 17 years ago when Johnson walked into her IBM office and told her he was leaving to go to upstart Microsoft. He asked her if she would take him back if he screwed up. Little did Johnson know — or Elliott either — that he would rise to head Microsoft’s biggest business, Windows, and one of its toughest, search.

For a decade, Johnson tried to hire Elliott at Microsoft. But she was a bleed-Blue loyalist. Caving in 2001, she flew from Connecticut to Seattle on September 10. Her first day at Microsoft was 9/11. Between running the company’s enterprise business in the Americas, co-heading the Americas organization, and leading the global Public Sector, Elliott handled some of Microsoft’s largest customers–which include countries and government agencies.

After she left in January, she followed the advice of a good friend: She didn’t take headhunter calls for two months. “I wanted and needed this break with my daughter,” Elliott, 53, told me in an email today. But the phone didn’t stop ringing, and eventually she considered CEO positions at start-ups, a president post at a Fortune 500 company,and COO and EVP jobs at several tech companies.

The only thing that really excited her was working with Johnson again. “He’s an exec who cares about the whole person,” she says — and he proved his worth by agreeing to put in Elliott’s Juniper employment contract that she’ll be able to go to the Fortune Most Powerful Women Summit. That’s the annual confab that I chair, and yes, I was shocked when Elliott told me that this event is so important to miss.)

Also in Elliott’s new contract: permission to participate in the annual Fortune – U.S. State Department Global Women Leaders Mentoring Partnership. This is a program that brings rising-star women from developing countries to shadow American women who participate in the MPWomen Summit. Since we launched the program in 2006, Elliott has been one of the program’s most supportive mentors.

So Johnson has lured Elliott to Silicon Valley by tailoring the job to her. The other clincher, she says: Juniper values partnerships. “I mean really values them, like it’s in their DNA,” she says. Elliott will hit the ground running and work to fortify the networking giant’s existing partnership with Nokia , Siemens and IBM.  Actually, she’s hard at work already. When I checked in with her earlier today, she was on the road with Johnson, visiting a Fortune 500 giant and trying to strike another major alliance. — Pattie Sellers