It actually sounds to me like the first nap might have been OS. It could have been UT, but if she was getting fussy before the nap and you struggled to keep her up til 10, I wonder if it wasn't OS and then she just woke straight and needed to get that out a bit. Since you just stretched to 3hr A, I'd keep there for a few more days and see what happens. One day doesn't offer much in terms of sleep patterns.
Yes, she was likely quite OT after the pm nap as she had a HUGE A time after not a very long nap in the morning. She might not have looked tired, because those 3-4min in the stroller made a difference for her. Or, she might have gotten her 'second wind' and was more 'happy tired', i.e. OT.
Should I force her to sleep even if she is looking OK and she is chatting and playing???
You never can really force a LO to sleep, but the beauty of Tracy's methodology is that you know your baby, so you keep an eye on the clock and an eye on her cues. You knew she had only a short morning nap, so with an average A of 3hr, she was probably ready for a nap again about 2-2.5hr later (likely when you were out for your walk). The more you BW, the more you'll know what different things 'look like'; what she is like when she's well rested and content, what she's like when she's tired and needing a nap, and what she's like when she's OT and seems happy and playing, but is really a bit over-happy. But, don't feel bad, we all miss it sometimes and even when we know all that we still make mistakes. It'll rarely be perfect, but you'll figure more and more things out as you go along.