You're most likely feeling grit in her crop, small rocks and stones that birds eat to help grind food in their Gizzard.  They will feel like corn bits, but it could also be corn.  To help with the Sour Crop part, she'll need to be started on Probiotics to combat the yeast that's building up in her Crop.  Yogurt and Probiotic water (Sav-A-Chick brand) are what we use to fend off Sour Crop when crop problems begin, but they both work well to neutralize the fermentation that's taken place.
Crop massages and oil (Coconut, Mineral, Olive, or even Vegetable) may help break the impaction and get things moving, but realize that your bird is 6-7 years old and also approaching end of life.  When end of life nears, systems can begin to shut down.  I know that's not what you want to hear, but it's the reality of birds that have life spans that usually don't exceed 7 or 8 years.
Crop bras may work, but I believe you'll only see success if regular Crop Massages are working to move food along.  If you're massaging and the food is NOT moving, then the bra is likely not going to be effective either.  Chicken Crops start to lose some of their elasticity and ability to "squeeze" food into the Proventriculus as birds age.
Having dealt with a fatal issue that was partially crop related with a prized girl brought on by ingestion of metal just in the last few weeks, I'd highly recommend a vet visit to be sure what you're dealing with.  X-rays (radiographs) are very telling.  She may have an issue further down the digestive tract.  Sadly, that's not a viable option for many due to the prohibitive costs - been there, done that!
Last, this is a good guide to help with Crop issues, and there is a load of information on the rest of the web:
https://www.backyardchickens.com/ar...w-to-know-which-one-youre-dealing-with.73607/