Yes, I think that's a good plan. Some babies do best with only a 5-10min bump at a time. She does sound a little sensitive and that's just fine. It will just take her a little bit to get used to a new A time. This is a hard age for naps for lots of reasons, but keep working on it, you'll get there.
And, you're right, often it's implied that poor naps come from OT, but UT can cause just as many problems. We've based our advice on seeing lots of babies in the same situation and given the fact that she did sleep longer on 1.15 and then started sleeping shorter again, means she needs a bit more. It's also good to always keep the averages in mind. At 4mo, the average A is 1.45-2hr. She may need a little less, some babies need more. So, if you're getting short naps on less than average, logic says to increase the A. Does that make sense?