Without knowing your style here’s what I would pick for a woman in her mid 50s at a lake wedding. https://www.nordstrom.com/s/belted-sleeveless-linen-blend-maxi-dress/8047898 https://www.nordstrom.com/s/faux-wrap-midi-dress/8152047 https://www.nordstrom.com/s/connected-apparel-tie-belt-faux-wrap-high-low-dress/7681007 https://www.nordstrom.com/s/floral-pleated-midi-dress/7982135 Polka dot: https://www.anthropologie.com/shop/the-jocelyn-sleeveless-slip-midi-dress-by-maeve https://www.nordstrom.com/s/donna-karan-new-york-print-sleeveless-midi-dress/7708276 https://www.anthropologie.com/shop/en-saison-monet-puff-sleeve-square-neck-midi-dress https://www.lillypulitzer.com/daphnie-tunic-dress/019274.html https://www.adriannapapell.com/products/sleeveless-floral-organza-wide-leg-jumpsuit-in-peri-coral-multi-ap1e211981 More on reddit.com

u/AssignmentCharming28 , thank you for posting. To obtain the best help, provide a time frame of the event & dress code. Dress links are frequently requested as well if you would place them in the comment section. I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns. More on reddit.com

Honestly, the number of times i dont think of macys first then get last minute guest dress for reasonable prices there is wild. If you're US based. I've done well at tj maxx and marshalls. Though that can be area dependent. Otherwise lulus, nordstrom, Karen millen ((though a bit more expensive on the expensive) hello molly, asos, oh polly, abercrombie is a good option, sometimes you can get lucky on revolve- they have some good options under $200 but def on the trendier side I'll try and think of more places. But I'd start with macys, abercrombie, lulus and nordstrom More on reddit.com

Dia & Co has some lovely options, largely by Kiyonna. Lace Dress - This would be pretty in sapphire, pinot noir, or, if you want to go with a summery color, coral. (I feel like September is a month where you can go summer or fall, depending on when during the month the event happens.) Second Lace Option - In addition to the shades you're trying to avoid (black and navy), this one comes in a lighter blue and the same coral as the first one. Third Lace Option - These lace dresses are all similar, but with different necklines and details. This one is really pretty, too, and comes in coral, indigo blue, plum wine, and ruby. I think the plum wine is such a pretty color if you're looking to go with a fall color. Fourth Lace Option - I'm not sure if this waist is too high for you, but I think the berry bliss color is so pretty for fall! Lace and Satin Dress - This dress in burgundy is definitely appropriate for a cocktail wedding! Embroidered Floral - In my experience, dresses similar to this one have become very popular for wedding guests. If you're willing to do black with a print/embroidery, I think this one is really pretty! Portrait Neckline - If you're comfortable wearing a strapless bra, I love this dress with a portrait neckline. Ruched Dress - I have this in black and I love the fit! I know you're not looking to wear black, but it also comes in a lovely pink. City Chic also has some great options! Strapless Ruffle - The available sizes are limited, but, if you're willing to go strapless, I think this is so pretty in garnet. Floral Print - This is the same dress as above, but in floral. It does have a black base, but the print is a large bold floral, so, if the bridesmaid dresses are solid black, it would look nothing like the bridesmaid dresses. Another Floral Option - This looks very similar to the above dresses, but I think the material is slightly different. The print is lovely! Tie Dress - This is lovely in the lighter blue! It's kind of close to navy, but, since your sister has expressed that she doesn't mind you wearing navy, I don't think it's a big deal if you wear a color that's navy-adjacent. Jumpsuit - If you want to be bold, a jumpsuit could be fun, and, as long as it's the appropriate level of formality, is appropriate for a cocktail dress code. I know jumpsuits may be different for someone your height, though. Chain Belt - It's possible I'm too into purple, but I really love the color of this one, and I think the included belt is fun, too! Reformation and BooHoo also have some lovely plus size options, though, admittedly, Reformation's sizes are more limited - up to a 3X, but I have found that their pieces run small, especially if you have a larger chest, so their 3X likely fits like a 2X in some other brands. More on reddit.com