G Tres / Splash News 1 / 6
G Tres / Splash News 1 / 6

Is Nicole Richie finally ready to become Mrs. Joel Madden? Signs are pointing to an imminent aisle-walk for the couple of nearly four years.

Over the weekend, the mom of Harlow, 2 1/2, and Sparrow, 1, reportedly had a combination bachelorette party and birthday celebration at a swanky resort in Cabo San Lucas, Mexico, with a passel of pals.

RELATED VIDEO: Nicole rocks a hot pink bikini

The group included Samantha Ronson and Christina Aguilera, who was photographed wearing a custom-made T-shirt that read, "Nicole's Bachelorette 9/17/10" on the back and the saucier "Tickle your chi chis with Miss Richie" on the front.

Further evidence that Nicole, who at one point showed off her fabulous (and now refreshingly height-weight appropriate) figure in only a pair of bikini bottoms, was enjoying a free-spirited good time before walking down the aisle: E! Online says she was seen out to dinner sporting a "bride-to-be" sash and a novelty necklace decorated with -- hmmmm, what's the best way to put this? -- plastic replicas of a certain important part of the male anatomy.

RELATED VIDEO: Katy Perry's sexy bachelorette shindig with Rihanna

Reps remain mum on whether the wedding is around the corner (or if Nicole's still-trouble-courting former BFF, Paris Hilton, is invited), although it seems unlikely that Richie, 29, and Madden, 31, who revealed their engagement in February, will tie the knot this weekend.

The Good Charlotte front man is scheduled to make a promotional appearance on Saturday at a Macy's in Minnesota.

RELATED: Nicole designs 'dream' engagement ring

Meanwhile, if Richie is feeling any stress over the nuptial planning, she wasn't showing it as she stepped out with Joel and Sparrow on Tuesday -- her actual birthday -- for lunch and shopping in Los Angeles.

"Wow I am feeling the love today!" she tweeted. "Thank you for all your birthday wishes! Here's to more wrinkles!!"

RELATED: Nicole won't reveal wedding details to dad Lionel

Speaking of wrinkles, there was apparently one big one during the special south-of-the-border getaway.

The New York Post says Lindsay Lohan "went crazy" trying to discover just who was on vacation with possibly back-on squeeze Ronson. Because that's what she should be worried about at this particular point in time.

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