V.Y.
I actually had the same exact thing happen. I asked advice from non biased parties and the consensus was to try and just phase the friendship out, unfortunately when you've been such close friends it's virtually impossible to have a discussion about having simply grown apart and wanting to 'break up' without it going really bad. So I did start to phase it out, which really is easier once you have kids and meet new mommy friends, tend to have so much less valuable spare time anyway it's easy to make the excuses. She definitely got the clue, and although it's so much nicer not having to deal with all the tension, irritation and uncomfortableness that comes with hanging out with her these days, we still have to cross paths with mutual friends. Those times, thankfully in large groups, are still uncomfortable, but few and far between. But unfortunately there really is no tried and true way to do it, it's gonna be a little messy either way. Good luck!