It seems like your supply is quite well established by now and I don't think there is anything wrong with using a dummy for kids who have a strong sucking drive. My DD was like that, some nights she just wanted a boob in her mouth continuously. Unfortunately for me, she didn't like the dummy, so I let her have the boob. it was the only way. And it didn't bother me nearly as much as a sleepless night would have. I slept quite well that way.
At about 6 months she all of a sudden accepted a dummy, and boy was I happy about that.
Some "experts" these days actually recommend a dummy over thumb or hand sucking because a dummy can be "controlled". You can give it to her only for sleep (which is what I mostly do, although she also gets it for car rides). And if you want to wean her off it, you can take it away. You can't take away her thumb!

Some babies just have a much stronger need for sucking. A friend of mine swore that she wouldn't use a dummy. At 4 months she figured that she was putting her own ambitions ahead of her daughters needs. her little girl had such a strong sucking reflex and was just generally a lot happier once the dummy was introduced. She felt bad for a while, but has soon gotten over the guilt and found that she had a much nicer time with her daughter.

Having said all that, your nipples will get used to all the "attention". So it won't be sore forever. And a little top up feed (although she might not be sucking hard) is nothing bad either. So I say, do what works for you. Give her the dummy without a bad conscience, if that's what she wants. Yes, eventually you will need to take it off her, but until then, why not use it.
I would only urge you to use the dummy in a controlled manner. Not just giving it to her all day, but using it in those tired moments to help her drop off to sleep. Make sure she isn't wanting to suck for food, as this could mess with your supply. Be sure she has lots of boobie time, too. Even when she just does "fairy sucks", it still stimulates your supply.

You are a great mum. Don't let anybody make you feel otherwise.
All the best, Saša