Charlotte,
I just have a couple of questions. I'm not sure if I will have any answers though.
How many times is she getting the bottle and the breast during 24hours? Is there any way why you do not want to bf during the day or is because she was not interested? If you wanted to keep up the one feed a day, would you be willing to pump to increase your supply or do feel more that if she cannot nurse just the once, it may be her time to wean?
I do know moms that have been able to keep up one feed a day. I'm not sure if everyone can. I never feel full anymore and I nurse 4 times a day, but only nursing once, it may actually be that your supply is dwindling, but I do not know that for sure. I do not have experience with this.
I also wanted to say that it's great that your lo was able to bf for so long. Thing of all the wonderful things you have provided for her. A big round of applause for you!!!!! Do not feel guilt please. You have done such a great thing for your lo. And who doesn't like a nice tank top without big ol grandma straps hanging out of it?? LOL