I've been blessed with healthy dogs so this observation only applies if Miss Memphis is healthy: I've always tried to keep my dogs a little bit on the lean side, and as long as I'm successful they have never been picky about their food. The only times I have ever seen any evidence of pickiness, it's corresponded to somebody getting a bit too sleek.
I've fed my last two dogs raw from puppyhood, but I've switched around a lot as far as sometimes using bagged frozen stuff, sometimes assembling meals myself from the grocery store, etc..
So -- if Miss M is on the sleek side, try cutting back on portion size or even fasting her for 12-24 hours. Again this assumes she's healthy, but it won't hurt her and may be what you need to whet her appetite enough so she'll try something new.
Dogs, by my observation, are scavengers by nature so switching to new foods really ought to be something that they take in stride. If Miss M is older of course she may have lost that tendency to some degree . . . and I know dogs with health issues e.g. thyroid can sometimes go off food . . .