Hi Amy!
Do you do a DF?
One thing I did with my two, as I was so reluctant to intro solids early, but also insistent that they STTN as they had been doing from 10 and 14 weeks respectively was to feed them on waking so they would get one full boob without even noticing as they were still semi-comotose - I would lift them from the cot with breast ready to latch onto straight away (TMI sorry). This meant much longer (and such cozy) feeds at 11 and 3pm as these were so distracted otherwise and then a DF straight from the breast with Emma at 11pm meant she continued to STTN.
In saying that though, Emma STTN from 10 weeks consistently but had a bad week at the 3 mth mark of waking at 3am again to feed (GS) and again a bad few days at the 4 mth mark so it could be just GS territory. If she is very hungry I would try the semi-comotose almost DF style feeding partic at 11am and 3pm, see does it help and then if it seems to you should see a gradual stretch back at nighttime.
I wouldn't go giving the breast at nap time if she is going a good 4 hrs btw feeds daytime, just try getting those exact feeds to be more calorific so that she tanks up daytime only.
The avatar is so so cute btw.
S x