My first advice is too try & be more relaxed about it... I got very anxious with my first & it was all a nightmare & this time around, I'm like, ok he won't nap, lets go for a walk, at least he is relaxed then & we are doing pretty well.
Now you actually do have a routine there, sure it drifts a bit, but that is ok, it shouldn't actually be by the clock, what the key is for your lo to know what comes next & also that you know that she fed 2 hours ago, so it isn't a hunger cry, it's a tired cry etc.
Now I'm a bf mum, but my understanding from my friends who ff, your lo would be best feeding every 4 hours to get a good feed in & my lo who is about 10days younger than yours is doing 3.5/4 quite easily (5 feeds/24 hours) & bf is slower to digest, I would suggest trying that & feed 6.30, 10.30, 2.30 & 6.30 + df but you can do it +/- 1/2 hour... more frequent feeds don't always equal longer night sleep when they get older!!!
Re the naps, now it is normal for babies to have an unsettled period each day & late afternoon is common, have you tried giving her a bath before that last nap of the day, although if you get her on a 4 hour routine, she wouldn't really need the 4th nap.
Now what do you do for activity time, because you may well be over stimulating... less is certainly more at this age. with both my boys, I would give tummy time, cuddles & a short (5min) activity like a book, but most of the time, they spent looking around on a mat & no more than 10mins under the play gym. I have rarely kept Liam up until he is cranky & if he is cranky it is nap time, even if he's been up only 1/2hour, the more you keep them up the more overtired & the less sleep you actually get.
Now with naps, you saying your awake time is about 1.5 hours or slightly less & your lo is cranky before naps, well at 1 hour, you should go into low stimulation mode, just let her lie on a mat on the floor or in a seat (not doing anything) Cuddle in quiet place, or soft talking, effectively starting a wind down, you could even do some baby massage, you want your lo to be relaxed & infact what you could do, which would help you is to sit her on your lap & cuddle & you do some breathing relaxation excercises... breath into count of 3 & out to 3, repeat a few times, then do it to 4, repeat, then 5, etc up to about 7... I do it up to 10 when I am trying to get to sleep & I'm overtired. As you relax so will your lo, because she is picking up all your anxiety (& trust me from your post you sound VERY anxious, so she is too)
Also how do you put her down for naps/bed time... do you use a paci?/swaddle? as a Paci may also be a problem.
HTH, feel free to field other questions