I have 2 friends who had dc, who refused solids until well into their 7month, if she isn't showing interest, she probably isn't ready... with one friend her ds was over 24lb & still wouldn't take solids, but when he did, he caught up very quickly & had mashed food within weeks of starting.
I'd just offer her it every day (about 1/2 hour after a bf) & don't make a drama out of it if she shuts her mouth, you can't force her, she will get there when she is ready, being bf, she is getting the nutrients she needs & she will be a very good judge of her humger & nutrient needs.
The only other suggestion is to try a bit on your finger & see if she sucks it off, then you will know if it is taste related or just no interest. If you have tried the plain rice with expressed breast milk then my guess is she just isn't interested yet as most babies who are interested will go for the taste of bm as they know it