Last year our BBB females started laying eggs at about that age as well. Not too old to process. Like stated above they are usually pretty tender even up to a year. I also make sure to age my turkeys in the fridge for 2-4 days prior to cooking or freezing them to let the enzymes work on tenderizing the meat. There is a big difference between aged and not that we have noticed.
Keep in mind that with the BBB you may not get to keep the layer too long, they can often have health problems related to their fast growth. You could save her from slaughter only to have her die of heart problems a couple of months later. (Not that she couldn't last a lot longer). I would just be hesitant to save one. If anything I would raise a heritage breed to keep around. Although I understand the attachment factor when they are sweet birds. Biggest thing if you are going to try to keep her is keep her from getting too heavy and put her on a layer ration.
I know you don't have boys, but the biggest problem we have experienced with keeping them a little longer is the males will injure the girls when trying to mate due to their size. Last years girls ended up with tears on both sides of their back from the males claws. I felt so bad for them, we didn't even notice the wounds until we plucked them! Live and learn I guess.