I'm glad I'm able to help! I'm a little sleep deprived due to baby's ear infection last night, so I'm never sure if what I say makes sense when I'm like this!
At 3.5 months old, most babies are starting to transition from 3 hour EASY to 4 hour EASY. Some go to a 3.5 hour easy as they adjust to going longer between feeds. Tracy recommends that you don't let your baby sleep longer than 2 hours during the day (at least at this young age - once you move to one nap, your child might sleep 2.5 hours), so that your LO keeps the difference between daytime and nighttime sleeps. A 2 hour nap at this age is the perfect length, so way to go LO!
I think at that age, Owen was going to a 4 hour EASY, and we pretty much went straight to 4 hours because he was ready. His A time was about 1.75-2 hours, so he'd be awake for around 2 hours, sleep for 2 hours, etc. We also had a 45 minute cat nap at the end of the day.
A good routine at this age would be:
7am wake/eat
9-11 nap
11 am wake/eat
1 pm-3 pm nap
3 pm wake/eat
4:45-5/5:30 nap
7:30 bed
I think you are going to find this adjustment very easy. Sounds like LO is textbook or angel, and very adjustable. The fact that you have a 1.5-2 hour awake time right now is perfect for make the change to a 3.5-4 hour EASY. And, you were able to get her to take a 2 hour nap, so she is able to do it! That's FABULOUS! Lots of moms would kill for that! You're at an age where 30-45 minute naps become a tough hurdle to get over, so you are doing beyond wonderful!
Anyway, try letting her nap as long as she needs (no more than 2 hours though), and then feeding her. Like I said, she may not eat as much as you'd like at the first feed or two, but by the end of the day my guess is she'll make up the difference with a couple of large feedings. That's how my DS was. His first 2 feeds of the day were relatively small, but his last 2 feeds were very large (I think he was taking 6-7 oz at that age for 1-2 bottles!), so in the end it worked out. We had a dream feed at 10/10:30 (which it sounds like you're doing), and then that was it for the night! I also had a luscious chunky monkey - he was 17 lbs at 4 months old - so, I know the worry that their little tummies will empty before the night is done. But, my guess is you'll be fine by just adjusting the feeds.
My only other suggestion is to make sure that the nipple size is the correct one on the bottles, especially if she's used to being BF. At 3 months old, we had to change to size 2 nipples because size 1 were too slow. What would happen is that he'd get bored with how long it was taking, and so would take a short feed. When we switched to size 2, he started taking full feeds again because he could eat fast enough. There was an adjustment period with a little bit of glugging and choking, which I solved by starting the feed with Size 2, ending it with Size 1 once he started choking.
Hope that helps!